trepidation n.

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" (source also of Greek tremein "to shiver, tremble, to quake, to fear," Lithuanian tremiu, tremti "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.

"unmoved by danger, undaunted," 1690s, from French intrépide (16c.) and directly from Latin intrepidus "unshaken, undaunted, not alarmed," from in- "not" (see in- (1)) + trepidus "alarmed," from PIE *trep-(1) "to tremble" (see trepidation). Related: Intrepidly; intrepidness (1620s).

"trembling from fear or terror," 1640s, from Latin trepidus "scared" (see trepidation). Related: Trepidly; trepidness.