Gap seen in old enclosure in front of garden (7)
I believe the answer is:
opening
'gap' is the definition.
(I know that gap can be written as opening)
'old enclosure in front of garden' is the wordplay.
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'enclosure' becomes 'pen' (pen is a kind of enclosure).
'front of' says to take the initial letters (the letter at the front of the word).
The initial letter of 'garden' is 'g'.
'o'+'pen'+'in'+'g'='OPENING'
'seen in' acts as a link.
(Other definitions for opening that I've seen before include "premiere" , "Window of opportunity" , "Orifice; opportunity" , "break" , "Space, gap; beginning" .)