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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]
persevere (v.): mid-14c., from Old French perseverer "continue, persevere, endure" and directly from Latin perseverare "continue steadfastly, persist," from persevereus "very strict, earnest," from per- "very" (see per) + severus "strict" (see severity). Related: Persevered; persevering.
persist (v.): 1530s, from Middle French persister (14c.), from Latin persistere "abide, continue steadfastly," from per- "thoroughly" (see per) + sistere "come to stand, cause to stand still" (see assist). Related: Persisted; persisting.
steadfast (adj.): Old English stedefæst "secure in position, steady, firm in its place," from stede (see stead) + fæst (see fast (adj.)); similar formation in Middle Low German stedevast, Old Norse staðfastr "steadfast, firm; faithful, staunch, firm in one's mind." Of persons, in English, "unshakable, stubborn, resolute" from c. 1200. Related: Steadfastly, steadfastness.