soft pedal vs foot pedal

soft pedal and foot pedal both are nouns.

Word	Noun	Adjective	Verb	Adverb
soft pedal	Yes	No	No	No
foot pedal	Yes	No	No	No

As nouns, foot pedal is a hypernym of soft pedal; that is, foot pedal is a word with a broader meaning than soft pedal:

soft pedal: a pedal on a piano that moves the action closer to the strings and so soften the sound
foot pedal: a lever that is operated with the foot

Other hypernyms of soft pedal include foot lever, pedal, treadle.

soft pedal (noun)	foot pedal (noun)
a pedal on a piano that moves the action closer to the strings and so soften the sound	a lever that is operated with the foot