intrepid: [17] The -trepid of intrepid represents Latin trepidus ‘alarmed’ (source also of English trepidation [17]), which goes back to an Indo- European source in which the notion of ‘fear’ seems to be linked with or derived from that of ‘scurrying away’. Addition of the negative prefix in- produced intrepidus ‘undaunted’, which reached English partly via French intrépide. => trepidation[intrepid etymology, intrepid origin, 英语词源]
1620s (implied in intrepidness), from French intrépide (16c.) and directly from Latin intrepidus "unshaken, undaunted," from in- "not" (see in- (1)) + trepidus "alarmed" (see trepidation). Related: Intrepidly.