Lack of verve in Florida, given temperature along cape (8)
I believe the answer is:
'lack of verve' is the definition.
The answer and definition can be both human attributes as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'florida given temperature along cape' is the wordplay.
'florida' becomes 'fla' (abbreviation).
'given temperature along' becomes 't' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'cape' becomes 'ness' (synonyms).
'in' is the link.
Can you help me to learn more?
(Other definitions for flatness that I've seen before include "Even quality" , "singers aim to avoid?" .)