[xīn bù zài yān]
be absent-minded; absence of mind; absent-mindedness; be woolgathering; be out to lunch; in a brown study; inattentive; One's wits are woolgathering.; One's wits are gone woolgathering.; One's mind is not in it.; One's mind was occupied with other things.; One's heart was no longer in it.; preoccupied; preoccupied with one's thought elsewhere; with an abstracted air; with one's mind wandering
listen absentmindedly
心不在焉地听着
His thoughts were far away and he didn't hear a word of what you said.
他心不在焉， 你说什么他都没听见。