die Uhr
clock / watch
An instrument that shows the time, for example a wristwatch or a wall clock.
Meine Uhr geht fünf Minuten vor.
My watch is five minutes fast.

clock / watch
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clock / watch
An instrument that shows the time, for example a wristwatch or a wall clock.
Meine Uhr geht fünf Minuten vor.
My watch is five minutes fast.

The word 'Uhr' (clock/watch) has two main functions. With an article ('die Uhr'), it refers to the device that measures time. Without an article, it is used as a unit for clock time and always comes after a number.
Ich brauche eine neue Uhr, meine alte ist kaputt.
I need a new watch; my old one is broken.
To indicate an exact point in time, the preposition 'um' (at) is almost always used. The fixed structure is: 'um + number + Uhr'.
Der Film beginnt pünktlich um 20:15 Uhr.
The film begins punctually at 8:15 p.m.
There are two important questions to distinguish. 'Wie viel Uhr ist es?' asks for the current time. 'Um wie viel Uhr?' asks for the time of an event.
Entschuldigung, wie viel Uhr ist es?
Excuse me, what time is it?
When 'die Uhr' (the clock/watch) refers to the device, it is often combined with certain verbs. Typical examples are: 'eine Uhr tragen' (to wear a watch), 'die Uhr stellen' (to set the time), or, when it is not working correctly: 'die Uhr geht vor/nach' (the clock/watch is fast/slow).
Meine Uhr geht jeden Tag zwei Minuten nach.
My watch is two minutes slow every day.
hour
'Uhr' and 'Stunde' both have to do with time, but they do not mean the same thing. 'Uhr' is used with a number when giving an exact time of day, for example '8 Uhr' (8 o'clock). 'Stunde' is a duration of 60 minutes. Learners often confuse the words because numbers occur in both cases. The difference is: 'um 8 Uhr' (at 8 o'clock) gives the point in time, while 'acht Stunden' (eight hours) gives the length of a period of time.

Der Unterricht beginnt heute um acht Uhr.
Class starts at eight o'clock today.
Für die Hausaufgaben brauche ich heute nur eine Stunde.
I only need one hour for the homework today.