expression, godan verb (-su)
listen carefully; strain one's ears
Used when one focuses intently on hearing faint or distant sounds.
See also: 澄ます (すます)
夜の森で、彼は耳を澄ましてフクロウの鳴き声を聞こうとした。
In the forest at night, he strained his ears to try to hear the owl's call.
Standard kanji spelling.
Kana spelling of 澄ます is common in this expression.
Implies actively trying to overhear something, often with a sense of eavesdropping, while 耳を澄ます is neutral and simply means listening attentively.
From 耳 (ear) + を + 澄ます (to make clear, to focus). The verb 澄ます here means to sharpen or concentrate one's hearing.