Stick up this clock (3)
I believe the answer is:
mug
'this clock' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'stick up' is the wordplay.
'stick' becomes 'gum' (I've seen this before).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'gum' back-to-front is 'MUG'.
Can you help me to learn more?
(Other definitions for mug that I've seen before include "A drinking vesel or a slangy victim" , "Large cup without a saucer" , "Make a face" , "Drinking vessel for one easily deceived" , "A person easily deceived, by gum" .)