the word 'tendon' entered english in the 1540s from the medieval latin term 'tendonem', which itself was derived from the late greek word 'tenōn', meaning 'sinew' or 'tendon'. this greek term is a nominal derivative of the verb 'teinein', which means 'to stretch'. the semantic logic is direct: a tendon is the part of the muscle that stretches and pulls. the greek root 'ten-' (to stretch) is part of a widespread proto-indo-european family, ten- 'to stretch', which also gives us english words like 'tension', 'extend', and 'tone'.

the word is a simplex loanword from latin and greek. it is not productively segmented using its modern english spelling.