pleatyoudaoicibaDictYouDict[pleat 词源字典]
pleat: [14] Pleat, plait, and plight ‘predicament’ are essentially the same word, but have become differentiated over the centuries. All three go back to Vulgar Latin *plicitum or *plictum ‘fold’, a noun use of the past participle of Latin plicāre ‘fold’ (source of English ply). This became Old French pleit, which was originally borrowed into English as plete ‘fold’. Plete was to become modern English pleat, but at first it was used only as a verb.

For the noun, English borrowed pleit as plait [15] ‘fold’, which did not begin to acquire its modern English meaning ‘braid’ until the 16th century. The Anglo- Norman version of pleit was plit, which gave English plight [14]. This too originally meant ‘fold’, and the sense ‘predicament’ was presumably due to the influence of the other (completely unrelated) English word plight (see PLEDGE), which as a noun in Old and Middle English meant ‘danger’, but is now mainly encountered in the expression ‘plight one’s troth’.
=> fold, plait, plight, ply[pleat etymology, pleat origin, 英语词源]
pleat (v.)youdaoicibaDictYouDict
1560s, used as the verb version of plait (n.) and probably representing an alternative pronunciation. Related: Pleated; pleating.
pleat (n.)youdaoicibaDictYouDict
"a fold," 1580s, variant of plait (n.). With a gap in the printed record 17c.-18c., but probably it was in continuous oral use.