noun, noun which may take the genitive case particle 'no'
two legs; two feet
Used for counting limbs or feet of living creatures, or for bipedal things.
人間は二足で歩く。
Humans walk on two legs.
二足歩行のロボットを開発している。
They are developing a bipedal robot.
noun, noun which may take the genitive case particle 'no'
two pairs (of footwear)
Used when counting pairs of shoes, socks, etc. The counter 足 (そく) is for footwear.
靴を二足買った。
I bought two pairs of shoes.
この店では二足目が半額になる。
At this store, the second pair is half price.
One pair of footwear; 二足 is two pairs.
Literally 'two legs', but more colloquial and often used for animals or objects standing on two legs.
Compound of 二 (two) and the counter 足 (そく) for pairs of footwear or legs. The reading にそく is standard.