아프다 -- to hurt, to be sick. Due to this dual meaning of "painful", "injured", and "sick", it can be the source of transference errors made by Koreans speaking English. For example, they may "My knee is sick" when they get a scrape.

Being an adjective this is an intransitive verb.

목이 아파요 My throat hurts.

언니가 아픕이까? Is your older sister sick?