As nouns the difference between downtime and undertime
is that downtime is the amount of time lost due to forces beyond one's control, as with a computer crash while undertime is (informal) the time spent at a workplace doing non-work activities.
downtime
English
Noun
(
en noun)
The amount of time lost due to forces beyond one's control, as with a computer crash.
A break or rest from work; leisure time.
- I've been working all weekend. I need some downtime .
undertime
English
Noun
(-)
(informal) the time spent at a workplace doing non-work activities.