Part of domain name for hostelry (3)
I believe the answer is:
inn
'hostelry' is the definition.
('inn' can be a synonym of 'hostelry')
'part of domain name for' is the wordplay.
'part of' indicates a hidden word.
'INN' is hidden within 'domain name for'.
(Other definitions for inn that I've seen before include "Possibly Jamaica" , "Drinking-place" , "Local" , "Roadhouse" , "Pub with lodging" .)