Stare intently before old boy returns to summerhouse (6)
I believe the answer is:
gazebo
'summerhouse' is the definition.
(synonyms)
'stare intently before old boy returns' is the wordplay.
'stare intently' becomes 'gaze' (to gaze is to stare intently at something).
'before' says to put letters next to each other.
'old boy' becomes 'OB' (abbreviation for a private school 'old boy').
'returns' says the letters should be written backwards.
'ob' back-to-front is 'bo'.
'gaze'+'bo'='GAZEBO'
'to' is the link.
(Other definitions for gazebo that I've seen before include "Summerhouse - pavilion with view" , "outhouse" , "Summerhouse with views" , "garden feature" , "Belvedere" .)