expression, i-adjective
Describes a state of inner turmoil or disquiet, often used when one's mind is not at peace due to worry, anger, or agitation.
彼の無礼な態度に心中穏やかでなかった。
I was upset by his rude attitude.
試験の結果が気になって、心中
I'm uneasy because I'm worried about the exam results.
心穏やかでない is a variant with the same meaning, using 心 (こころ) instead of 心中 (しんちゅう). Both are used, but 心中穏やかでない is slightly more formal.
A set phrase composed of 心中 (しんちゅう, 'in one's heart/mind') + 穏やかでない (the negative form of 穏やか, 'calm, peaceful'). Literally 'not calm in one's heart'.