'armlock' originates from English compounds 'arm' and 'lock'. 'arm' ultimately comes from Old English 'earm' meaning 'arm', and 'lock' comes from Old English 'locc' meaning 'a fastening' or 'to fasten'.

'arm' (Old English 'earm') + 'lock' (Old English 'locc') were combined in modern English to form the compound 'arm-lock'/'armlock' (attested in sporting contexts from the 19th–20th century), which stabilized into the single-word form 'armlock' in some usages.

Initially the elements referred literally to 'an arm' and a 'locking' or fastening; over time the compound came to mean specifically 'a hold that locks or immobilizes the arm' in combat-sport contexts.