sandal vs flip-flop

sandal and flip-flop both are nouns.

Word	Noun	Adjective	Verb	Adverb
sandal	Yes	No	No	No
flip-flop	Yes	No	Yes	No

As nouns, flip-flop is a hyponym of sandal; that is, flip-flop is a word with a more specific, narrower meaning than sandal:

sandal: a shoe consisting of a sole fastened by straps to the foot
flip-flop: a backless sandal held to the foot by a thong between the big toe and the second toe

Other hyponyms of sandal include espadrille, thong, huarache, huaraches, pusher, zori, scuffer, talaria.

sandal (noun)	flip-flop (noun)
a shoe consisting of a sole fastened by straps to the foot	a backward somersault
	an electronic circuit that can assume either of two stable states
	a backless sandal held to the foot by a thong between the big toe and the second toe
	a decision to reverse an earlier decision

sandal (verb)	flip-flop (verb)
	reverse (a direction, attitude, or course of action)