diagram vs Venn diagram

diagram and Venn diagram both are nouns.

Word	Noun	Adjective	Verb	Adverb
diagram	Yes	No	Yes	No
Venn diagram	Yes	No	No	No

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

diagram: a drawing intended to explain how something works; a drawing showing the relation between the parts
Venn diagram: a diagram that uses circles to represent mathematical or logical sets pictorially inside a rectangle (the universal set); elements that are common to more than one set are represented by intersections of the circles

Other hyponyms of diagram include block diagram, horoscope, schematic, schematic drawing, Venn's diagram, zodiac.

diagram (noun)	Venn diagram (noun)
a drawing intended to explain how something works; a drawing showing the relation between the parts	a diagram that uses circles to represent mathematical or logical sets pictorially inside a rectangle (the universal set); elements that are common to more than one set are represented by intersections of the circles

diagram (verb)	Venn diagram (verb)
make a schematic or technical drawing that shows interactions among variables or how something is constructed