The Compendium of Caraka 6.21.40

6.21.40

upadravastu khalu rogottarakālajo rogāśrayo roga eva sthūlo 'aṇurvā, rogāt paścājjāyata ityupadravasaṃjñaḥ/

A complication indeed is a condition arising after a disease, based on that disease, and is itself a disease, gross or minute; because it arises after the disease, it is given the name 'complication'.