Wiry means thin but strong and tough. Not much of it, and none of it soft.
It describes bodies above all, and a wiry man is lean and surprisingly powerful, which is why the word suits climbers, jockeys and long-distance runners. It is a compliment. It also describes hair that is coarse and springy, and a wiry terrier has a rough coat. The image behind all of them is wire itself, which is thin and does not break. Its opposite for a physique is burly.
Proto-Indo-European
*weh₁y-
Proto-Indo-European
*weh₁iros — a twist, thread, cord, wire
Proto-Germanic
*wīraz — wire
Old English
wīr — wire, metal thread, wire-ornament
Middle English
wir
English
wire
English, today
wiry
Built from
From wire + -y. wire comes from Middle English wir, wyr, from Old English wīr (“wire, metal thread, wire-ornament”), from Proto-Germanic wīraz (“wire”), from Proto-Indo-European weh₁iros (“a twist, thread, cord, wire”), from weh₁y- (“to turn, twist, weave, plait”).
Etymology from Wiktionary, CC BY-SA