c. 1300, from after + noon. In 15c.-16c., the form was at afternoon; from c. 1600 it has been in the afternoon. Middle English also had aftermete "afternoon, part of the day following the noon meal," mid-14c.
1. They rose to the challenge of entertaining 80 school-children for an afternoon.
2. It was a marvellous afternoon with a huge turnout of people.
3. The President met this afternoon with his top military advisers.
4. It happened at Stamford Bridge one murky November afternoon.
5. The fighting began in the late afternoon and continued all night.