Old English strengþu, strengð "bodily power, force, vigor, firmness, fortitude, manhood, violence, moral resistance," from Proto-Germanic *strangitho (source also of Old High German strengida "strength"), from PIE *strenk- "tight, narrow" (see string (n.)), with Proto-Germanic abstract noun suffix *-itho (see -th (2)). Compare length/long. From the same root as strong,
Entries linking to strength
Old English meaning "ligaments, tendons" is preserved in hamstring (n.), heart-strings. Meaning "limitations, stipulations" (1888) is American English, probably from the common April Fool's joke of leaving a purse that appears to be full of money on the sidewalk, then tugging it away with an attached string when someone stoops to pick it up.
To pull strings "control the course of affairs" (1860) is from the notion of puppet theater. First string, second string, etc. in athletics (1863) is from archers' custom of carrying spare bowstrings in the event that one breaks. Strings "stringed instruments" is attested from mid-14c. String bean is from 1759; string bikini is from 1974.
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fatigue sapped his strength
we faced an army of great strength
it was destroyed by the strength of the gale
the strength of his argument settled the matter
they measured the station's signal strength
the strength of the drinks
the strength of the company's stock in recent weeks