melodic theme vs motif

melodic theme and motif both are nouns.

Word	Noun	Adjective	Verb	Adverb
melodic theme	Yes	No	No	No
motif	Yes	No	No	No

As nouns, motif is a hyponym of melodic theme; that is, motif is a word with a more specific, narrower meaning than melodic theme:

Other hyponyms of melodic theme include motive, statement, variation.

melodic theme (noun)	motif (noun)
(music) melodic subject of a musical composition	a design or figure that consists of recurring shapes or colors, as in architecture or decoration
	a unifying idea that is a recurrent element in literary or artistic work
	a theme that is repeated or elaborated in a piece of music