The H of mph (4)

I believe the answer is:
hour
(Other definitions for hour that I've seen before include "60 minutes" , "See 12" , "Sixty minutes" , "Time within day" , "Clock time" .)
I believe the answer is:
hour
(Other definitions for hour that I've seen before include "60 minutes" , "See 12" , "Sixty minutes" , "Time within day" , "Clock time" .)