gig mill vs gig-mill

gig mill and gig-mill both are nouns.

Word	Noun	Adjective	Verb	Adverb
gig mill	Yes	No	No	No
gig-mill	Yes	No	No	No

As nouns, gig mill and gig-mill are synonyms defined as:

gig mill and gig-mill: a textile mill employing rotary wire cylinders for napping.

gig mill (noun)	gig-mill (noun)
a textile mill employing rotary wire cylinders for napping.	a textile mill employing rotary wire cylinders for napping.