The hour (symbol: h) is a unit of time. It isn't an SI unit but is accepted for use with the SI. Definition In modern usage, an hour is a unit of time 60 minutes, or 3,600 seconds in length. It is approximately 1/24 of a median Earth day. Etymology Middle English ure first appears in the 13th century, as a loanword from Old French ure, ore, form Latin hora, ultimately from Greek "season, time of day, hour". Middle English ure, Anglo-French houre replaced Old English tíd (which survives as… (More on Hour)