sensei 先生

In Japanese, sensei 先生 means "teacher" most of the time. It can also mean "doctor," or refer to an artist or author, a "master" of arts. It's also a honorific, so it can come after the name of someone who's a teacher, doctor, artist, etc.

Manga: "Assassination Classroom," Ansatsu Kyoushitsu 暗殺教室 (Chapter 2, 野球の時間)

• Kanji
• "Teacher"
• "Master"
• "Doctor"
• "Author," "Writer," "Artist"
• After Name
• せんせー

Kanji

The kanji of sensei 先生 mean "previous," 先, and "life," 生.

Source: japanesewithanime.com (CC BY-SA 4.0)

• sensei
  先生
  Teacher.
  • sen 先 and sei 生are on'yomi readings..
• {saki ni umareta} hito
  先に生まれた人
  Person [who] {was born earlier}.
  • saki 先 and umu 生む are kun'yomi readings.

Of course, it's not always the case that your sensei is older than you, but that's just where the word comes from.

せんせー

The word sensee せんせー is a relaxed pronunciation of sensei. It means the same thing, it's just spelled differently, pronounced more casually, and not the proper way to spell the word.

Manga: School Rumble, スクールランブル (Chapter 3, Deep Space Nine)

• sensee
  せんせー
  Teacher.
• nanda?
  なんだ？
  What is it?
• {me ga warui} node
  mae no seki to
  koukan shite
  hoshii-n-desu-ga
  目が悪いので前の席と交換してほしいんですが
  [I have poor eyesight] so [I] want to switch [with one of] the front seats.
  • me ga warui
    目が悪い
    Eyes are bad. (literally.)
    To have poor eyesight.
    (double subject construction with body part.)

"Teacher" in Japanese

The word sensei 先生 can mean "teacher" in Japanese, and it can be used by a teacher as first person pronoun when talking to their students.

Manga: "Assassination Classroom," Ansatsu Kyoushitsu 暗殺教室 (Chapter 2, 野球の時間)

• Context: Koro-sensei 殺せんせー, a teacher, talks to Shiota Nagisa 潮田渚, one of his students.
• sensei wa ne, Nagisa-kun
  先生はね　渚君
  Nagisa-kun, [about me], [you see]
  • In this line, the speaker is the teacher, the sensei.
  • When he talks "about the sensei," he's talking about himself: "about me."
• {aru hito to no yakusoku wo
  mamoru} tame ni
  kimi-tachi no sensei ni
  narimashita
  ある人との約束を守るために君達の先生になりました
  In order to keep a promise with a [certain] person {[I've] become your teacher}.
  • kimi-tachi no
    君達の
    Your. (plural, as the teacher "of you students.")

There are other words that can also refer to teachers, for example:

• kyoushi
  教師
  Teacher.
  • Who teaches in a:
  • kyoushitsu
    教室
    Classroom.
  • Can also refer to a teacher as in someone who offers guidance in a:
  • kyoukai
    教会
    Church.
  • senkyoushi
    宣教師
    Missionary.
• katei kyoushi
  家庭教師
  Family teacher. (literally.)
  Private tutor.
• tan'nin kyoushi
  担任教師
  Teacher in charge.
  • The teacher who's in charge of a classroom, also known as "homeroom teacher."
  • tan'nin no sensei
    担任の先生
    (same meaning.)
• kyouin
  教員
  Faculty member.
  • Any "educator" from grade school to high school.
• kyouyu
  教諭
  Licensed teacher.
  • Someone with a license to teach in a school.
• kyouju
  教授
  Professor.
  • Specially of an university, or college, daigaku 大学, as opposed to high-school and below.
• hakase
  博士
  Professor. PhD. Doctor.
  • In anime, these are often researchers, inventors, scientists, not teachers.

"Master" in Japanese

The word sensei 先生 may also refer to a "master," in the sense that they're an expert in their field or craft and you can learn from them, even if they aren't in fact officially teaching anyone as a normal teacher would.

Manga: Majin Tantei Nougami Neuro 魔人探偵 脳噛ネウロ (Chapter 1, 手【て】)

• Context: just... just focus on the dialogue, okay?
• boku wa joshu desu!!!
  僕は助手です！！
  I'm an assistant!!
• kono meitantei
  Katsuragi Yako-sensei no!!
  この名探偵桂木弥子先生の！！
  Of this famous detective, Katsuragi Yoko-sensei!!
  
  • She's a famous detective, because of her incredible detective skills, so she's addressed as a "master" of her craft.
  • The no の at the end turns the noun into a no-adjective, which normally qualifies what comes after it, but, in this case, it qualifies joshu, which is in a previous sentence.
  • sensei no joshu
    先生の助手
    Sensei's assistant.
    Assistant of sensei.
  • The dots on the furigana of 名探偵 express emphasis.

There are also other words for "master" in Japanese:

• shishou
  師匠
  Master. (e.g. of martial arts.)
• goshujinsama
  ご主人様
  A retainer's lord.
  A slave's master.
  A pet's owner.
  A shop's owner.
  A woman's husband.
• masutaa suru
  マスターする
  To master. (a skill.)

"Doctor" in Japanese

The word sensei 先生 may also refer to a "doctor."

Manga: MONSTER, モンスター (Chapter 7, モンスター)

• Context: a doctor talks to a patient in wheelchair, who is also a criminal.
• ningen wa yari-naoseru.
  人間はやり直せる。
  Humans can do-over.
  Humans can [start again].
  
  • yari-naoseru - potential verb.
  • yari-naosu
    やり直す
    To do over.
    To do something again.
  • yaru
    やる
    To do.
• ima kara demo osokunai......
  いまからでも遅くない･･････
  Even from now isn't late......
  • You can still start over, it isn't too late to begin now.
• sensei......
  先生･･････
  Doctor......
• sensei to ore,
  anmari toshi
  chigawanai kedo............
  先生と俺、あんまり年違わないけど････････････
  [You] and me, [our] ages don't differ much, but.........
  • We're about the same age, but...
• sensei...... oyaji mitai da.
  先生･･････親父みたいだ。
  [You]...... are like [my] father.

There are other words used to refer to doctors, for example:

• isha
  医者
  Doctor.
• oishasan
  お医者さん
  Doctor. (polite variant.)
• ishi
  医師
  Doctor (certified.)
  • The difference between ishi 医師 and isha 医者 is that an isha is a "doctor" in the sense that they're treating patients, while ishi 医師 is literally a "master of medicine."
  • That is, ishi 医師 puts emphasis on knowledge and expertise, and, perhaps most importantly, on their medical certification, their medical license.
  • In manga, sometimes you have black market doctors who don't have a license but go around treating people. Those would be isha, but not ishi.

"Author," "Writer," "Artist" in Japanese

The worse sensei 先生 can also refer to authors, writers of fiction, novels, and artists, painters, illustrators, etc.

In the manga and anime Bakuman バクマン, for example, Ashirogi Mutou 亜城木夢叶 is the pen name used by the two main characters on the manga they author. It's not even a real name, it's just a pseudonym. Even so, they are still called Ashirogi-sensei 亜城木先生 by other characters in the series because their skill and knowledge in the field has been deemed real.

There are other words for this stuff:

• sakka
  作家
  Author.
• shousetsu-ka
  小説家
  Novelist. Fiction writer.
  • Writes:
  • shousetsu
    小説
    Novel.
• manga-ka
  漫画家
  Manga artist.
• ga-ka
  画家
  Painter.
• irasutoreetaa
  イラストレーター
  Illustrator.

Honorific

When sensei 先生 comes after a person's name, it means that person is a sensei. That is: that person is a teacher, or a doctor, or an artist, or a writer, etc. For example:

• watashi no sensei
  私の先生
  My teacher.
  • Here, sensei is a noun.
• Tanaka-sensei
  田中先生
  Tanaka (who's a teacher.)
  Teacher Tanaka.
  • Here, sensei is a honorific.
• watashi no sensei wa Tanaka-san
  私の先生は田中さん
  My teacher is Tanaka-san.
• {sensei ni osowatta} koto wa isshou wasurenai
  先生に教わったことは一生忘れない
  What {teacher taught [me]}, [I] will [never] forget.
  • isshou wasurenai
    一生忘れない
    To not forget through one's whole life.
    To never forget.
• {Tanaka-sensei ni osowatta} koto wa isshou wasurenai
  田中先生に教わったことは一生忘れない
  What {Tanaka-sensei taught [me]} [I] will [never] forget.

When this sort of thing happens, it's called a honorific. In Japanese, when a noun is used as a honorific, it means that person is that noun. This often happens with titles of professions. An example of another noun honorific:

• watashi no senpai
  私の先輩
  My senior.
• Tanaka-senpai
  田中先輩
  Tanaka (who's my senior.)

• Tanaka-hakase
  田中博士
  Tanaka (who's a professor.)
  Professor Tanaka.
• Tanaka-shishou
  田中師匠
  Tanaka (who's my master.)
  Master Tanaka.
• Tanaka-oniisan
  田中お兄さん
  Tanaka (who's my older brother.)
  Big bro Tanaka.