noun, noun which may take the genitive case particle 'no'
one foot; one leg
Refers to a single foot or leg, often in contexts of balance, injury, or standing on one leg.
He is standing on one leg.
He is practicing standing on one leg.
片足をけがして歩けない。
I injured one leg and can't walk.
one of a pair (of shoes or socks)
Only when written 片足
Used when referring to a single item from a pair, typically shoes or socks. Restricted to the 片足 spelling.
One of my socks has gone missing.
I injured one of my legs during the soccer match.
The child went outside wearing only one shoe.
片膝 uses the 片- prefix with 膝 (knee) to mean one knee, while 片足 uses the same prefix with 足 (leg/foot) to mean one leg, so learners may mix up which body part is meant.
standing on one leg; single-leg stance
Standard kanji spelling; used for both 'one foot/leg' and 'one of a pair' senses.
Alternate kanji spelling emphasizing the leg rather than the foot; less common than 片足.
Compound of 片 (kata, 'one side') + 足 (ashi, 'foot/leg'). The reading かたあし is a straightforward combination of the kun'yomi readings.