In Japanese, yosa 良さ, also spelled yosa よさ, means "good-ness" or "how good it is." It's the sa-form, "-ness form," of the i-adjective yoi 良い, "good," and the de facto sa-form of its more common synonym, ii いい.

Don't mistake yosa 良さ with yosasou 良さそう, which means "it seems it's good," or with the expression yossha! よっしゃ！, "alright!"

• Examples

In Japanese, kono hito, sono hito, ano hito この人, その人, あの人 mean literally "this person," "that person (near you)," and "that person (far from you)" respectively.

• Usage
  • なんだこの人？！

In Japanese, the phrases kono ko, sono ko, ano ko この子, その子, あの子 are used to refer to children, or to people the same age or younger than the speaker, or even to animals.

• Usage
• Examples

In Japanese, warui ko 悪い子 means a "bad kid," in the sense of a misbehaving, naughty child. It can also refer to a "bad," Warui 悪い, adult or animal, who's like a naughty kid—doing mischief and stuff—because of how Ko 子 works.

The antonym would be ii ko いい子, "good child."

• Usage
• Toward Adults
• Related Vocabulary

In Japanese, ii ko いい子, also spelled ii ko 良い子, means "good child," or "good kid." It can also be used toward adults, animals, etc. depending on context to say they're a "good," ii いい, person, animal, etc. See ko 子 for details.

The phrase yoi ko よい子 is a synonymous variant.

• Usage
  • いい子にしてた
  • いい子にしててね
• Malicious Usage

In Japanese, yosasou よさそう, also spelled yosasou 良さそう, means "looks like it's good." It's what you get when you add the sou そう suffix to the sa-form of the i-adjective yoi よい, "good." It's also de facto the sou-form of the synonym ii いい.

• 良さそうな
• 良そう vs. 良さそう

In Japanese, yoshi yoshi よしよし means "there, there," in the "it's alright, shh" sense used to comfort children, and sometimes to calm down crying children, etc.

Literally, yoshiyoshi means "alright, alright." It's the word yoshi よし, "alright," twice.

In Japanese, yossha よっしゃ means "ALRIGHT!!!" It's like the word yoshi よし, except that yossha is pretty much always used to shout and enthusiastically cheer while yoshi has other uses.

• Usage
• Variants

In Japanese, yoshi よし means "alright!" It's often an expressions used when you're ready to do something—"alright, let's go!"—or it can simply mean something is okay—"that's alright too."

Sometimes, it's pronounced yooshi よーし instead.

• Usage
  • これでよし
  • それもよし
  • よしとする
• Yoshi in Japanese

In Japanese, yokereba よければ, also spelled yokereba 良ければ, means "if you'd like to," or "if you want to."

• yokereba yonde kudasai
  よければ読んでください
  If you'd like, please read [it].
• Please read if you'd like.

It's basically synonymous with yokattara よかったら, the only difference being that yokereba is more polite.^{[「よければ」と「よかったら」の違いについて - detail.chiebukuro.yahoo.co.jp, 2019-02-13]}

Grammatically, yokereba is the ba-form of yoi よい.

In Japanese, yokattara よかったら, also spelled yokattara 良かったら, means "if that's alright with you," or "if you'd like," "if you feel like it," "if you want, "etc. It's generally used when you offer or propose something to someone, to ask whether they're okay with it.

Grammatically, yokattara よかったら is the tara-form of yoi よい, and of ii いい, so it's literally "if good."

• Explanation
• Examples
  • もしよかったら
  • 私でよかったら
  • よかったらどうぞ
  • よかったら来てほしい
  • よかったら仲良くしてください
• Expressions
• Synonyms
• 嫌なら

In Japanese, yokumo よくも means "HOW DARE YOU?!?!?!?!?!" most of the time. Technically, it's just the adverb yoku よく intensified by mo も, and as such it can be used when good things happen, too, but it's mostly used when bad things happens, specially in anime.

The word can also be spelled yokumo 善くも, although that's unusual.

• Explanation
• よくまあ, yoku maa
• Further Reading

In Japanese, yoku よ, also spelled yoku 良く, means literally that you've done "good" or have done "well," but it can also mean something happens "often" or "a lot," and it can also mean something is "impressive" to have done, often given unfavorable circumstances, or, also, because of the nerve you had to have to dare do it.

The word yoku よく is the adverbial form of ii いい, or rather, of yoi 良い. Note that yokunai よくない means "not good" instead, because to inflect the negative form of i-adjectives you add the auxiliary nai ない to the adverbial form. And yokute よくて is the te-form of the i-adjective.

• "To Do Well"
  • よくやった
  • よく頑張った
  • よく出来た
  • よく聞け
  • よく見ると
• よくそんな
  • "Hard to Believe You Did That"
  • "Ugh! I Would Never Do That!!! Don't You Have No Shame?!"
  • "You Peasant, Don't You Know Your Place?!"
• "Often"
  • "A lot"
• Expressions
• Grammar
• 良く, 善く, 能く, 好く, 克く

In Japanese, yokunai よくない, "not good," also spelled yokunai 良くない, is the negative form of ii いい, "good."

Fortunately, there isn't much special about it. It's just the negative of ii いい.

The word yokunakatta よくなかった would be "was not good," past negative. Technically, both yokunai and yokunakatta are inflections of the i-adjective yoi よい, not of ii いい, but ii is never inflected, ii and yoi are synonymous, and ii is more common, so they're de facto inflections of ii.

• "Not Good"
  • Yokunai vs Warui
• Yokunee よくねー, 良くねぇ, よくねー, 良くねぇ

In Japanese, warukunai 悪くない means literally "not bad," the negative form of warui 悪い, "bad." The word warukunai can also mean "it's not my fault" or "it's not his fault," since warui can be used to say something is something's fault. For the same reason, warukunai can also mean there's nothing "wrong" with something.

The word warukunakatta 悪くなかった, "was not bad," past negative form, would also work similarly but in the past.

• "Not Bad"
• "Not My Fault"
• "Nothing Wrong With This"