Pulpit used by Uppingham boys (4)
I believe the answer is:
ambo
'pulpit' is the definition.
(synonyms)
'used by uppingham boys' is the wordplay.
'used by' indicates a hidden word.
'AMBO' is hidden within 'uppingham boys'.
(Other definitions for ambo that I've seen before include "Where the preacher stood" , "Early Christian pulpit" , "desk" , "Raised pulpit" , "Old reading-desk" .)