oiler vs oil tanker

oiler and oil tanker both are nouns.

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

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

Other synonyms of oiler include tank ship, tanker.

oiler (noun)	oil tanker (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