gallon vs gal

gallon and gal both are nouns.

Word	Noun	Adjective	Verb	Adverb
gallon	Yes	No	No	No
gal	Yes	No	No	No

As nouns, gallon and gal are synonyms defined as:

gallon and gal: United States liquid unit equal to 4 quarts or 3.785 liters

gallon (noun)	gal (noun)
United States liquid unit equal to 4 quarts or 3.785 liters	alliterative term for girl (or woman)
a British imperial capacity measure (liquid or dry) equal to 4 quarts or 4.545 liters	United States liquid unit equal to 4 quarts or 3.785 liters
	a unit of gravitational acceleration equal to one centimeter per second per second (named after Galileo)