'uncap' originates from the English prefix 'un-' (from Old English 'un-') combined with 'cap' (Middle English 'cap(p)e') where the element 'cap(p)e' came from Late Latin 'cappa' meaning 'hood' or 'cloak'.

'cap' came into Middle English as 'cap(p)e' from Old North French/Old French 'cape' or Late Latin 'cappa'; the modern verb 'uncap' was formed in English by adding the productive negative or reversing prefix 'un-' to the noun/verb 'cap'.

Initially, related elements signified a hood or covering; over time 'cap' came to mean a head covering or lid, and 'uncap' developed to mean removing that cover (literally) and later extended figuratively to removing limits or ceilings.