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fastly (adv.)[fastly 词源字典]: "quickly," c. 1200, former adverbial cousin to fast (adj.), from Old English fæstlic "firmly, fixedly, steadfastly, resolutely;" obsolete in 19c., simple fast taking its place.[fastly etymology, fastly origin, 英语词源]
irresolute (adj.): 1570s, from Latin irresolutus, from assimilated form of in- "not, opposite of" (see in- (1)) + resolutus (see resolute). Related: Irresolutely.
resolute (adj.): early 15c., "dissolved, of loose structure," also "morally lax," from Latin resolutus, past participle of resolvere "untie, unfasten, loose, loosen" (see resolution). Meaning "determined, decided, absolute, final" is from c. 1500, especially in resolute answer, a phrase "common in 16th c." [OED]. From 1530s of persons. The notion is of "breaking (something) into parts" as the way to arrive at the truth of it and thus make the final determination (compare resolution). Related: Resolutely; resoluteness.