Number of winding route in low-lying area (8)
I believe the answer is:
'number' is the definition.
(fourteen is a number)
'winding route in low-lying area' is the wordplay.
'winding' is an anagram indicator.
'in' is an insertion indicator.
'low lying area' becomes 'fen' (term for a marshy area).
'route' with letters rearranged gives 'ourte'.
'ourte' going within 'fen' is 'FOURTEEN'.
'of' is the link.
(Other definitions for fourteen that I've seen before include "XIV" , "Fen route (anag)" , "Number of lines in a sonnet" , "Pounds in a stone?" .)