'tendonless' is formed in Modern English by combining the noun 'tendon' with the suffix '-less' (from Old English 'lēas', meaning 'free from, without').

'tendon' itself comes into English via Old French 'tendon' from Latin roots related to 'tendō / tendere' meaning 'to stretch'; the adjectival suffix '-less' comes from Old English 'lēas'. These elements were compounded in Modern English to form 'tendonless'.

The compound originally and straightforwardly meant 'without tendons' and has retained that literal anatomical meaning; any figurative uses (e.g., lacking structural support) are derived later.