dapper: [15] Modern English dapper connotes neatness, alertness, and liveliness, but its etymological significance as revealed by distant relatives such as Old High German tapfar ‘heavy’, Old Prussian debīkan ‘large’, and Old Slavic debelu ‘thick’, is ‘heavy’. The notion of ‘weightiness’ spread to ‘firmness, endurance in battle’, and hence ‘courage’ (German tapfer and Dutch dapper both mean ‘brave’). English acquired the word, with an apparently ironical change of meaning, from Middle Dutch or Middle Low German dapper ‘heavy, stout, bold’.
dapper (adj.)
mid-15c., "elegant," from Middle Dutch or Middle Low German dapper "bold, strong, sturdy," later "quick, nimble," from Proto-Germanic *dapraz, perhaps with ironical shift of meaning (cognates: Old High German tapfar "heavy," German tapfer "brave"), from PIE root *dheb- "dense, firm, compressed."