One thread among those twisted into a larger cord. A strand is weak alone and is what the rope is made of.
Probably kin to Old English streng (a string, a cord), from Proto-Germanic *strangi-; the exact path by which strand reached English is not fully settled, though its closeness to string is.
One thread among those twisted into a larger cord, weak alone and exactly what the rope is made of. Kin to string, the way a single line is kin to the whole of it.