一言

Noun

 * 1)  one sentence; something to say; brief remark
 * 2)  one character

Etymology 1
From compound. The goon, so likely the initial borrowing.

Noun

 * 1) a (single) word, a few words

Idioms

 * : “to cover this with one word/phrase” → to sum up complicated details in a few short words
 * : “not even a word” → to be speechless; to have nothing to say
 * : “one word on phrase” → word by word, distinctly
 * : “one word half a phrase” → word by word, distinctly
 * : “a word once said is hard to catch even with a four-horse team”

Derived terms

 * : a person who must speak their mind about everything
 * : a traditional poem wherein a single character is used to fit the meter of a whole line

Verb

 * 1) to say a few words

Etymology 2
Shift in pronunciation from ichigon above, using the kan'on of gen for the character.

Noun

 * 1) a (single) word, a few words

Idioms

 * : “to cover this with one word/phrase” → to sum up complicated details in a few short words

Derived terms

 * : one action and one word
 * : a person who must speak their mind about everything

Verb

 * 1) to say a few words

Etymology 3
Compound of.

Noun

 * 1) a (single) word, a few words

Idioms

 * : “a word [too] many” → to say too much, to say something better left unsaid