1580s, "pertaining to a place;" see topic + -al (1). Medical sense "applied to a particular part of the body" is from c. 1600. Meaning "of or pertaining to topics of the day" is from 1873. Related: Topically.
a drug for topical (or local) application
a topical anesthesia
a detailed record on both a chronological and a topical basis
a topical and timely study of civil liberty
a topical reference