Origins
The word 'covert' entered Middle English from Old French 'covert,' the past participle of 'covrir' (to cover, to conceal), which descended from Latin 'cooperΔ«re' (to cover completely, to overwhelm).βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ The Latin verb compounds 'co-' (an intensive prefix meaning 'thoroughly') with 'operΔ«re' (to shut, to cover, to close). To be covert is, at the etymological level, to be thoroughly covered β hidden from sight, concealed beneath a layer of disguise or secrecy.
The relationship between 'covert' and 'cover' is straightforward: both come from Old French 'covrir,' but 'cover' entered English as a verb (to place something over) while 'covert' entered as an adjective (in a state of being covered). They are doublets β two English words from the same foreign source that arrived through slightly different grammatical paths.
The antonym 'overt' has a parallel etymology that creates a satisfying symmetry. 'Overt' comes from Old French 'overt' (open, uncovered), the past participle of 'ovrir' (to open), from Latin 'aperΔ«re' (to open, to uncover). Where 'cooperΔ«re' means to cover thoroughly, 'aperΔ«re' means to uncover. The covert/overt pair thus preserves in English an opposition that was already present in Latin between 'cooperΔ«re' and 'aperΔ«re.'
Development
In medieval English, 'covert' had both literal and legal meanings. Literally, a 'covert' was a shelter β a thicket or dense vegetation where animals could hide. This sense survives in hunting and ornithological vocabulary: game birds break from 'covert' (the underbrush). In law, 'coverture' was the legal doctrine by which a married woman's legal identity was subsumed ('covered') by her husband's β she was a 'feme covert' (a covered woman), with no independent legal existence. This doctrine persisted in English common law until the nineteenth century and was one of the primary targets of early feminism.
The modern dominant sense of 'covert' β secret, clandestine, hidden from public knowledge β became prominent in the twentieth century through military and intelligence usage. 'Covert operations' are missions conducted secretly, without public acknowledgment by the government that authorizes them. The CIA's covert operations during the Cold War β from the 1953 Iranian coup to the Bay of Pigs invasion β made 'covert' a word freighted with political controversy. The distinction between 'covert' (secret but authorized) and 'clandestine' (secret in its execution) is technically precise in intelligence terminology, though the words are often used interchangeably in common speech.
A surprising relative is 'curfew,' from Old French 'covrefeu' β literally 'cover fire' (covre + feu). In medieval towns, a bell was rung in the evening as a signal to bank or cover one's hearth fire, both to prevent accidental conflagrations and to mark the beginning of nighttime hours when people were expected to be indoors. The word migrated from 'cover your fire' to 'the evening bell' to 'the time at which people must be indoors,' which is its modern meaning.
Legacy
'Discover' is another important relative: 'dis-' (un-) + 'cover' = to uncover, to reveal what was hidden. Discovery is etymologically the removal of a cover β the exposure of something that was covert. This chain β cover, covert, discover β traces a narrative arc: something is hidden (covered), it exists in a state of secrecy (covert), and then it is found (discovered, uncovered).