Hour
Definition 1 of 4
Pro Tip 1/3
Duration Reference
Use 'hour' when indicating the length of time something takes. The test will last an hour.
Pro Tip 2/3
Approximation
'About an hour' implies a rough estimate, not exactly 60 minutes. I'll be back in about an hour.
Pro Tip 3/3
Common Phrases
'On the hour' means when the clock strikes a full hour. The show starts on the hour.