oil tanker vs oiler

oil tanker and oiler both are nouns.

Word	Noun	Adjective	Verb	Adverb
oil tanker	Yes	No	No	No
oiler	Yes	No	No	No

As nouns, oil tanker and oiler are synonyms defined as:

Other synonyms of oil tanker include tank ship, tanker.

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