three legs; two legs and a cane
Often used figuratively to describe an elderly person walking with a cane, as in the saying 'a person has three legs in old age'.
The old man is walking slowly with a cane (literally, on three legs).
Compound of 三本 (three long, thin objects) and 足 (leg). The reading さんぼん is a regular rendaku form of さんほん.