Florida island's mood -- everything depends on it (8)
I believe the answer is:
keystone
'florida' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'island's mood everything depends on it' is the wordplay.
I cannot really see how this works, but
'island's' could be 'keys' and 'keys' is present in the answer.
'mood' could be 'tone' (tone is a kind of mood) and 'tone' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for keystone that I've seen before include "everything may depend on it" , "Central part of arch" , "Central policy; arch top" , "Important piece at apex of arch" , "supporter?" .)