Rarely stands alone in modern Mandarin — usually appears in compounds: 衷心 (sincerely), 由衷 (heartfelt), 苦衷 (difficulties one cannot easily explain), 无动于衷 (unmoved).
memory
The character is 中 ("middle / center") wedged inside 衣 ("clothing"): originally an undergarment "in the middle of the clothes" → by extension, what is innermost in a person → inner feelings.
