adverb
pleasantly; comfortably; agreeably
Describes doing something in a way that feels good physically or emotionally; often used with verbs like 眠る, 過ごす, 話す.
温泉に入って気持ちよく過ごした。
I spent a pleasant time soaking in the hot spring.
新しい布団で気持ちよく眠れた。
I slept comfortably on the new futon.
adverb
willingly; readily; without complaint
Used when someone does something with a positive attitude, without reluctance; often with verbs like 引き受ける, 手伝う, 応じる.
彼は気持ちよく頼みを引き受けてくれた。
He willingly took on the request.
気持ちよく手伝ってくれてありがとう。
Thank you for helping so readily.
Adverbial form of 気持ちいい (気持ち + いい), literally 'feeling good'. The adverbialization follows the regular pattern of changing いい to よく.