Is it farther or further?
c.1300, "shake from fear, cold, etc.," from Old French trembler "tremble, fear" (11c.), from Vulgar Latin *tremulare (source of Italian tremolare, Spanish temblar), from Latin tremulus "trembling, tremulous," from tremere "to tremble, shiver, quake," from PIE *trem- "to tremble" (cf. Greek tremein "to shiver, tremble," 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.