良い

Modern form of Old Japanese adjective よし (yoshi).^[1][2][3]

/joɕi/ (classical 終止形 (shūshikei) or terminal form) → /joki/ (classical 連体形 (rentaikei) or attributive form) → /joi/ (modern shūshikei and rentaikei)

• (classical Japanese) よし (yoshi), えし (eshi)
• (standard Japanese, more informal) いい (ii)
• (literary) えい (ei)
• (dialect) ええ (ē)

• (Tokyo) よい (Atamadaka – )^[2][4]
• IPA^(key):

良(よ)い • (yoi) -i (adverbial 良(よ)く (yoku))

1. good

   Antonyms: 悪い, 駄目

• Most often written in hiragana. The kanji spelling is generally reserved for more formal writing.

• When with the そう (-sō) suffix, it is よさそう (yosasō) instead of よそう (yosō).

• 頭(あたま)が良(よ)い (atama ga yoi), 頭(あたま)がよい (atama ga yoi): bright, intelligent

良(よ)い • (-yoi) 

1. easy

   分かり良い ― wakariyoi ― easy to understand

• Most often written in hiragana. The kanji spelling is generally reserved for more formal writing.
• Attaches to the 連用形 (ren'yōkei, “continuative or stem form”) of a verb. Example:

  読(よ)み良(よ)い ― yomiyoi ― easy to read

However, in modern Japanese, the adjective 安い, 易い (yasui, “easy, easygoing”) is more commonly used to express this meaning.

Phonetic shift from the Old Japanese yoshi form of yoi above. Already in use as early as the Nihon Shoki, circa 720,^[1][2][3] then becoming common in eastern Japanese from the Edo period.^[2] This form is now obsolete, though it may still be found in some dialects.

/joɕi/ (classical 終止形 (shūshikei) or terminal form) → /eɕi/ (classical 終止形 (shūshikei) or terminal form) → /eki/ (classical 連体形 (rentaikei) or attributive form) → /ei/ (modern shūshikei and rentaikei)

• IPA^(key):

良(え)い • (ei) -i (adverbial 良(え)く (eku))

1. (obsolete) good

Phonetic shift from ei above. This is now the most common form used in casual spoken Japanese.^[1][2][3]

/ei/ → /ii/

• (Tokyo) いい (Atamadaka – )^[2][4]
• IPA^(key):

• Audio:

  (file)

良(い)い • (ii) -i (adverbial 良(よ)く (yoku))

1. (colloquial, informal) good
2. (colloquial, predicative only) enough; not wanted any more.

   酒(さけ)はもういい

   sake wa mō ii

   I have had enough wine/I don't want any more wine.

• Most often written in hiragana. The kanji spelling is generally reserved for more formal writing.
• The ii form does not inflect — it is only used in the 終止形 (shūshikei, “terminal form”) and 連体形 (rentaikei, “attributive form”) of ii. All other grammatical forms are based on the yoi form above. Compare the 連用形 (ren'yōkei, “continuative or adverbial form”) yoku or the 過去形 (kakokei, “past tense”) yokatta: there is no *iku or *ikatta form.
• In ironic usages denoting "very bad; embarrassing", the ii form is preferred to the yoi form.

• 頭(あたま)が良(い)い (atama ga ii), 頭(あたま)がいい (atama ga ii): bright, intelligent