diesel vs diesel motor

diesel and diesel motor both are nouns.

Word	Noun	Adjective	Verb	Adverb
diesel	Yes	No	No	No
diesel motor	Yes	No	No	No

As nouns, diesel and diesel motor are synonyms defined as:

diesel and diesel motor: an internal-combustion engine that burns heavy oil

Other synonyms of diesel include diesel engine.

diesel (noun)	diesel motor (noun)
an internal-combustion engine that burns heavy oil	an internal-combustion engine that burns heavy oil