Length of short gap year rearranged around beginning of December (7)
I believe the answer is:
yardage
'length' is the definition.
(I've seen this before)
'short gap year rearranged around beginning of december' is the wordplay.
'short' means to remove the last letter.
'rearranged' indicates an anagram.
'around' means one lot of letters goes inside another.
'beginning of' says to take the initial letters.
The first letter of 'december' is 'd'.
'gap' with its final letter taken off is 'ga'.
'ga'+'year'='gayear'
'gayear' anagrammed gives 'yarage'.
'yarage' enclosing 'd' is 'YARDAGE'.
'of' acts as a link.
(Other definitions for yardage that I've seen before include "Amount of length (imperial)" , "Distance (eg in golf)" , "Distance sometimes measured in paces" , "charge for using court" , "Distance in three-foot units" .)