mid-14c., "remorse, contrition (for wrongdoing, as a means of attaining forgiveness of one;s sins)," from Old French compunction (12c., Modern French componction), from Late Latin compunctionem (nominative compunctio) "remorse; a stinging or pricking" (of the conscience), noun of action from past-participle stem of Latin compungere "to severely prick, sting," from com-, here perhaps an intensive prefix (see com-), + pungere "to prick, pierce" (from suffixed form of PIE root *peuk- "to prick").
The Latin word was used in a figurative sense by early Church writers. Originally a much more intense feeling, similar to "remorse," or "contrition."
word-forming element making adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from Old French -ous, -eux, from Latin -osus (compare -ose (1)). In chemistry, "having a lower valence than forms expressed in -ic."