Stick plug in this space (6)
I believe the answer is:
adhere
'stick' is the definition.
('adhere' can be a synonym of 'stick')
'plug in this space' is the wordplay.
I cannot quite see how this works, but
'plug' could be 'ad' (Advertisement plugs products) and 'ad' is found in the answer.
The remaining letters 'here' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for adhere that I've seen before include "Stick with header" , "Stick to or continue faithful" , "Stick to or remain faithful" , "Hold fast, stand by" , "'Stick to, a play say (6)'" .)