Definition of main-belt:
(adj) :
Of chief or leading importance; prime, principal.
(adj) :
Chief, most important, or principal in extent, size, or strength; consisting of the largest part.
(adj) :
(dialectal) Big; angry.
(adj) :
(nautical) Belonging to or connected with the principal mast in a vessel.
(adv) :
(British, dialectal) Exceedingly, extremely, greatly, mightily, very, very much.
(v) :
(transitive, gaming) To mainly play a specific character or side, or with specific equipment, during a game.