koi 来い, 恋, 鯉, 濃い

In Japanese, koi こい can mean different things depending on how it's spelled.

• 来い
• 恋
• 鯉
• 濃い

来い

The word koi 来い is the meireikei 命令形, "imperative form," of the irregular verb kuru 来る, "to come," which is opposite to iku 行く, "to go."

• kocchi ni koi
  こっちに来い
  Come here.
• acchi ni ike
  あっちに行け
  Go over there.

Since kuru 来る can be used as an auxiliary verb, so can koi 来い.

• yakisoba-pan katte koi
  焼きそばパン買ってこい
  Go buy a yakisoba bread and then come back here.
• benkyou shi-naoshite koi
  勉強し直してこい
  Go study [it] over again, then come back here.
  • Phrase probably used when someone hasn't studied something enough.
• hashitte koi
  走ってこい
  Go run, then come back here.
  Come here running.
• tonde koi
  飛んでこい
  Go jump, then come back here.
  Come here jumping.
• orite koi
  降りてこい
  Come here falling.
  Come down here.
• kakatte koi
  かかってこい
  Bring it on!
  • Phrase used when starting a fight with someone.

恋

The word koi 恋 means "love" in the romantic sense. It differs from ai 愛, for example, which means love in a more general sense, including familial sense, or divine sense.

More practically, koi 恋 is the sort of love that gets your heart-shaped pupils in anime, while ai 愛 does not.

• hatsu-koi
  初恋
  One's first love.
• {koi suru} otome
  恋する乙女
  A maiden [who] {loves [someone]}.
• koi ni ochiru
  恋に落ちる
  To fall in love.
• koibito
  恋人
  Lover. Partner.

The kanji is also read as ren 恋.

• ren'ai
  恋愛
  Romance.
• ren'ai mono
  恋愛もの
  Romance works. Romance stories. Romance manga, anime, movies, books, etc.
• shitsuren
  失恋
  Failed love. When the person you love doesn't love you back, and you have to give up on it.

鯉

The word koi 鯉 refers to the carp. The koi carp, Cyprinus carpio, which is a fish. In manga and anime, the carp is frequently used in visual puns when a character falls in love.

Anime: Uchi Tama?! Uchi no Tama Shirimasen ka? うちタマ？！～うちのタマ知りませんか？～ (Episode 2)

As well as in textual puns.

Manga: School Rumble, スクールランブル (Volume 1, Chapter ♭01 Wonder Woman)

• Context: Tsukamoto Tenma 塚本天満 sees her younger sister, Tsukamoto Yakumo 塚本八雲, packing a lunch box for someone. She guesses the food is for a boyfriend. It turns out she was just feeding a stray cat.
• zettai koi dato omotta noni
  絶対恋だと思ったのに～
  Even though [I] absolutely thought [it] was love...
  But [I] was sure [it] was [it] was love...
• koi...? neko dayo
  鯉･･･？猫だよ
  Carp...? [It] is a cat.

濃い

The word koi 濃い is an i-adjective which means a "strong" flavor or smell, or a "deep" color, or that something is "dense," or "thick" in consistency. It's antonym is usui 薄い, which means a "weak" flavor or smell, a "thin" consistency, and so on.

• koi aji
  濃い味
  Strong taste.
• koi nioi
  濃い匂い
  Strong smell.
• koi iro
  濃い色
  Deep color.
• koi ekitai
  濃い液体
  Thick liquid.
• koi gasu
  濃いガス
  Dense gas.

Although they have multiple translations in English, the basic idea is usui 薄い is when something feels "watered down," be it flavor, smell, color, and so on, while koi 濃い is the opposite of watered down.

In other cases, you wouldn't use koi and usui. You would use:

• tsuyoi
  強い
  Strong. Powerful.
• yowai
  弱い
  Weak.
• fukai
  深い
  Deep. Profound. (can be used toward colors.)
• asai
  浅い
  Shallow.
  Pale. (color.)
• atsui
  厚い
  Thick. (diameter.)
  • Not to be confused with:
  • atsui
    熱い
    Hot.
• hosoi
  細い
  Thin. (diameter.).