Flat number seventeen it's installed in (4)
I believe the answer is:
even
'flat' is the definition.
(similar in meaning)
'seventeen it's installed in' is the wordplay.
'in' indicates the answer is hidden within the clue.
'EVEN' can be found hidden inside 'seventeen installed'.
'number' acts as a link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for even that I've seen before include "Regular; calm" , "on level terms" , "Yet; smooth" , "Like 2018 but not 2017" , "time when sun goes down for the poet" .)