six o'clock

Short definition from Wiktionary

Noun

1. 1
   The start of the seventh hour of the day; 6:00 a.m. (06:00).
2. 2
   The start of the nineteenth hour of the day; 6:00 p.m. (18:00).
3. 3
   A position behind (horizontal clock orientation) or below (vertical clock orientation) (from the location of the 6 mark on a clock face)
4. 4
   A pose in which the lower leg and raised upper leg form a vertical line.

Adjective

1. 1
   Straight up and down, without curves, like the hands of a clock.