underside

n a supplementary feather (usually small) on the underside of the base of the shaft of some feathers in some birds

a saprophytic fungus of the order Agaricales having an umbrellalike cap with gills on the underside

land on the underside without the landing gear

v land on the underside without the landing gear

anglewing butterfly with a comma-shaped mark on the underside of each hind wing