gable wall vs pediment

gable wall and pediment both are nouns.

Word	Noun	Adjective	Verb	Adverb
gable wall	Yes	No	No	No
pediment	Yes	No	No	No

As nouns, pediment is a hyponym of gable wall; that is, pediment is a word with a more specific, narrower meaning than gable wall:

gable wall: the vertical triangular wall between the sloping ends of gable roof
pediment: a triangular gable between a horizontal entablature and a sloping roof

Other hyponyms of gable wall include bell gable, corbie gable.

gable wall (noun)	pediment (noun)
the vertical triangular wall between the sloping ends of gable roof	a triangular gable between a horizontal entablature and a sloping roof