set·back 
(sĕtbăk′)
(sĕtbăk′)n.
1. An unanticipated or sudden check in progress; a change from better to worse.
2.
a. A steplike recession in a wall. Also called setoff.
b. Any of a series of such recessions in the rise of a tall building.
3. An automatically timed setting of a thermostat to a lower temperature, as in the home at night.