tank ship vs oil tanker

tank ship and oil tanker both are nouns.

Word	Noun	Adjective	Verb	Adverb
tank ship	Yes	No	No	No
oil tanker	Yes	No	No	No

As nouns, tank ship and oil tanker are synonyms defined as:

tank ship and oil tanker: a cargo ship designed to carry crude oil in bulk

Other synonyms of tank ship include oiler, tanker.

tank ship (noun)	oil tanker (noun)
a cargo ship designed to carry crude oil in bulk	a cargo ship designed to carry crude oil in bulk