Speedily comes from speedy + -ly; speedy derives from speed, from Old English spēd ('success, swiftness'), from Proto-Germanic *spōdiz. The historical chain includes Old English spēd and Proto-Germanic *spōdiz. The quoted older sense, "success, swiftness," supplies the immediate semantic anchor for speedily. The formation is best read as suffixal and borrowed: the word speedily carries its older form-history into a compact English lexical shape. In present English it is used as a adv, "in a quick or rapid manner". Related English forms include speed, speedy, and speediness. The result is a adv whose etymology preserves both the older form and the later English specialization.