Informal second-person singular (tú) affirmative imperative form of incubar.
Formal second-person singular (usted) present indicative form of incubar.
Third-person singular (él, ella, also used with usted?) present indicative form of incubar.
Etymology
A respelling of incubus, substituting the (Latin second-declension nominative singular) masculine case ending-us with its (first-declension) feminine equivalent -a; compare succuba, succubus.