Trepidacious is a mis-spelling. Trepidatious would be close to etymology. Not in M-W dictionary.
Here's closest word:
Main Entry: trep·i·da·tion
Pronunciation: "tre-p&-'dA-sh&n
Function: noun
Etymology: Latin trepidation-, trepidatio, from trepidare to tremble, from trepidus agitated; probably akin to Old English thrafian to urge, push, Greek trapein to press grapes
1 archaic : a tremulous motion : TREMOR
2 : timorous uncertain agitation : APPREHENSION
synonym see FEAR