A writer figures they're mountains (9)
I believe the answer is:
apennines
'mountains' is the definition.
(I've seen this before)
'a writer figures' is the wordplay.
'writer' becomes 'pen' (I've seen this before).
'figures' becomes 'nines'.
'a'+'pen'+'nines'='APENNINES'
'they're' is the link.
(Other definitions for apennines that I've seen before include "Mountain range in central Italy" , "European range" , "Italian mountains" , "Italian mountain chain" , "Italian mountain range" .)