strong (adj.) Look up strong at Dictionary.com
Old English strang "physically powerful, powerful in effect; forceful, severe, firm, bold, brave; constant, resolute; arduous, violent," from Proto-Germanic *strangaz (cognates: Old Norse strangr "strong," Dutch streng "strict, rigorous," Old High German strang "strong, bold, hard," German streng "strict, rigorous"), possibly from PIE *strenk- "tight, narrow." Originally compared strenger, strengest (compare old/elder/eldest).

Grammatical sense, of noun and verb inflections, is first attested 1841, translating German stark, used in a grammatical sense by J. Grimm (the terms strong and weak better fit German inflections). Strong suit (1865) is from card-playing. Strong man "man of great strength" (especially one who displays it professionally) is recorded from 1690s; meaning "dominating man in a political organization" is from 1859.
strong (adv.) Look up strong at Dictionary.com
Old English strange "strongly, violently, severely, furiously" (alongside strongly), from the same source as strong (adj.). Going strong (1898) is from racing. To come on strong was originally come it strong (1812).