Dapper

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late Middle English: probably from a Middle Low German or Middle Dutch word meaning ‘strong, stout’.

wiktionary

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From Middle English daper(“pretty, neat”), from Middle Dutch dapper(“stalwart, nimble”), Old Dutch *dapar, from Proto-Germanic *dapraz(“stout; solid; heavy; bold”) (compare German tapfer "bold", Norwegian daper "saddened, dreary"), from Proto-Indo-European *dʰeb- ‘thick, heavy’ (compare Tocharian A tpär ‘high’, Latvian dàbls ‘strong’, Serbo-Croatian дебео(dèbeo) ‘fat’).

etymonline

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dapper (adj.)

mid-15c., "elegant, neat, trim," from Middle Dutch or Middle Low German dapper "bold, strong, sturdy," later "quick, nimble," from Proto-Germanic *dapraz (source also of Old High German tapfar "heavy," German tapfer "brave"), perhaps with ironical shift of meaning, from PIE root *dheb- "dense, firm, compressed."

Later shifting toward "small and active, nimble, brisk, lively" (from c. 1600). "Formerly appreciative; now more or less depreciative, with associations of littleness or pettyness" [OED].