play (something) by ear

US /pleɪ ˈsʌm.θɪŋ baɪ ɪr/
UK /pleɪ ˈsʌm.θɪŋ baɪ ɪr/
"play (something) by ear" picture
1.

臨機応変に対応する, ぶっつけ本番でやる

to decide how to deal with a situation as it develops, rather than by having a fixed plan

:
We don't have a set schedule for the trip; we'll just play it by ear.
旅行の決まったスケジュールはありません。臨機応変に対応します。
I can't give you a definite answer now, let's just play it by ear and see how things go.
今すぐ明確な答えは出せません。臨機応変に対応して、状況を見ましょう。
2.

耳で演奏する, 楽譜なしで演奏する

to play a piece of music without having seen it written down

:
She can play any song by ear after hearing it once.
彼女は一度聞いただけで、どんな曲でも耳で演奏することができます。
Many jazz musicians prefer to play by ear rather than read sheet music.
多くのジャズミュージシャンは楽譜を読むよりも耳で演奏することを好みます。