The Collaborative International Dictionary of English v.0.48:
Afternoon \Aft"er*noon"\, n. The part of the day which follows noon, between noon and evening. [1913 Webster]WordNet (r) 3.0 (2006):
afternoon n 1: the part of the day between noon and evening; "he spent a quiet afternoon in the park" 2: a conventional expression of greeting or farewell [syn: good afternoon, afternoon]