gully vs wadi

gully and wadi both are nouns.

Word	Noun	Adjective	Verb	Adverb
gully	Yes	No	No	No
wadi	Yes	No	No	No

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

gully: deep ditch cut by running water (especially after a prolonged downpour)
wadi: gully or streambed in northern Africa and the Middle East that remains dry except during rainy season

Other hyponyms of gully include arroyo, draw.

gully (noun)	wadi (noun)
deep ditch cut by running water (especially after a prolonged downpour)	gully or streambed in northern Africa and the Middle East that remains dry except during rainy season