Reveal boozer is supporting large hospital (7)
I believe the answer is:
publish
'reveal' is the definition.
(thesaurus)
'boozer is supporting large hospital' is the wordplay.
'boozer' becomes 'pub' (UK slang).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'large' becomes 'L' (eg in clothes sizes).
'hospital' becomes 'H' (abbreviation for hospital).
'is' put after 'l' is 'lis'.
'pub'+'lis'+'h'='PUBLISH'
(Other definitions for publish that I've seen before include "Report" , "Issue, make known" , "Get into print" , "Issue (a book/magazine)" , "Damned if I do!" .)