first gear vs low gear

first gear and low gear both are nouns.

Word	Noun	Adjective	Verb	Adverb
first gear	Yes	No	No	No
low gear	Yes	No	No	No

As nouns, first gear and low gear are synonyms defined as:

first gear and low gear: the lowest forward gear ratio in the gear box of a motor vehicle; used to start a car moving

Other synonyms of first gear include first, low.

first gear (noun)	low gear (noun)
the lowest forward gear ratio in the gear box of a motor vehicle; used to start a car moving	the lowest forward gear ratio in the gear box of a motor vehicle; used to start a car moving