uneasiness; anxiety; insecurity
A state of mental unease, worry, or lack of peace of mind. Used both as a noun and as a na-adjective.
I was so anxious about the exam results that I couldn't sleep at night.
He was pacing around the room with an uneasy look.
Compound of 不 (fu, 'not') + 安心 (anshin, 'peace of mind'). The exact historical derivation is uncertain, but the meaning is transparent from its components.