Servius on Virgil, Aeneid XII, 159, on the feminine gender of nouns ending in -tor: But if they are not derived from a verb they are common in gender. For in these cases both the masculine and the feminine end alike in -tor, for example, senator, a male or female senator, balneator, a male or female bath attendant, though Petronius makes an exception in speaking of a

bath-woman

( balneatricem).