oiler vs cargo vessel

oiler and cargo vessel both are nouns.

Word	Noun	Adjective	Verb	Adverb
oiler	Yes	No	No	No
cargo vessel	Yes	No	No	No

As nouns, cargo vessel is a hypernym of oiler; that is, cargo vessel is a word with a broader meaning than oiler:

Other hypernyms of oiler include cargo ship.

oiler (noun)	cargo vessel (noun)
a cargo ship designed to carry crude oil in bulk	a ship designed to carry cargo
a well that yields or has yielded oil
a worker who oils engines or machinery