big vs gravid

big and gravid both are adjectives.

Word	Noun	Adjective	Verb	Adverb
big	No	Yes	No	Yes
gravid	No	Yes	No	No

As adjectives, big and gravid are synonyms defined as:

Other synonyms of big include enceinte, expectant, great, heavy, large, with child.

big (adjective)	gravid (adjective)
above average in size or number or quantity or magnitude or extent	in an advanced stage of pregnancy
conspicuous in position or importance
given or giving freely
generous and understanding and tolerant
marked by intense physical force
significant
prodigious
serious or severe
loud and firm
(of animals) fully developed
in an advanced stage of pregnancy
feeling self-importance
exhibiting self-importance