expression, godan verb (-u)
talk in one's sleep
Literal meaning: to speak while asleep. Also used figuratively to mean saying something nonsensical or unrealistic.
彼はよく寝言を言う。
He often talks in his sleep.
そんなの寝言を言うようなものだ。
That's like talking nonsense.
Standard kanji spelling for the expression.
Mixed kana-kanji spelling; common in casual writing.
Kana spelling for 言う; often used when the verb is written in kana.
寝言 is the noun 'sleep-talking' or 'nonsense'; 寝言を言う is the verb phrase.
Compound of 寝 (ne, 'sleep') + 言 (koto, 'word') with rendaku, plus を言う (o iu, 'to say'). Literally 'to say sleep-words'.