buckle vs belt buckle

buckle and belt buckle both are nouns.

Word	Noun	Adjective	Verb	Adverb
buckle	Yes	No	Yes	No
belt buckle	Yes	No	No	No

As nouns, belt buckle is a hyponym of buckle; that is, belt buckle is a word with a more specific, narrower meaning than buckle:

buckle: fastener that fastens together two ends of a belt or strap; often has loose prong
belt buckle: the buckle used to fasten a belt

buckle (noun)	belt buckle (noun)
fastener that fastens together two ends of a belt or strap; often has loose prong	the buckle used to fasten a belt
a shape distorted by twisting or folding

buckle (verb)	belt buckle (verb)
bend out of shape, as under pressure or from heat
fasten with a buckle or buckles
fold or collapse