tremble: [14] Tremble goes back ultimately to a prehistoric base *trem- ‘shake’, which probably has connections with English terrify, terror, etc. Amongst the Latin descendants of this base were tremor ‘shaking’ (source of English tremor [14]), tremere ‘tremble’ (source of English tremendous [17]), and tremulus ‘shaking’ (source of English tremolo [19] and tremulous [17]). The last of these formed the basis of a Vulgar Latin verb *tremulāre, which passed into English via Old French trembler as tremble. => terrify, terror, tremendous, tremor, tremulous
tremble (v.)
c. 1300, "shake from fear, cold, etc.," from Old French trembler "tremble, fear" (11c.), from Vulgar Latin *tremulare (source also of Italian tremolare, Spanish temblar), from Latin tremulus "trembling, shaking, quaking," from tremere "to tremble, shiver, quake," from PIE *trem- "to tremble" (cognates: Greek tremein "to shiver, tremble, to quake, to fear," Lithuanian trimu "to chase away," Old Church Slavonic treso "to shake," Gothic þramstei "grasshopper"). A native word for this was Old English bifian. Related: Trembled; trembling. The noun is recorded from c. 1600.
