loud pedal vs foot pedal

loud pedal and foot pedal both are nouns.

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

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

loud pedal: a pedal on a piano that lifts the dampers from the strings and so allows them to continue vibrating
foot pedal: a lever that is operated with the foot

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

loud pedal (noun)	foot pedal (noun)
a pedal on a piano that lifts the dampers from the strings and so allows them to continue vibrating	a lever that is operated with the foot