one knee
Refers to a single knee, often used in set phrases like 片膝をつく (to kneel on one knee) or 片膝を立てる (to raise one knee).
He proposed on one knee.
I sat on the floor, raised one knee, and listened.
片膝 refers to only one knee, while 両膝 refers to both knees together, as in 両膝をつく (kneel on both knees).
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.
Standard kanji spelling.
Search-only kanji form; not a standard spelling.
Compound of 片 (kata, 'one side') + 膝 (hiza, 'knee').