Insanitary hospital locked up by nice guy in cast (10)
I believe the answer is:
unhygienic
'insanitary' is the definition.
(similar in meaning)
'hospital locked up by nice guy in cast' is the wordplay.
'hospital' becomes 'h'.
'locked up by' means one lot of letters goes inside another.
'cast' indicates an anagram (letters are dispersed or cast around).
'nice'+'guy'+'in'='niceguyin'
'niceguyin' with letters rearranged gives 'unygienic'.
'h' inserted within 'unygienic' is 'UNHYGIENIC'.
(Other definitions for unhygienic that I've seen before include "Dirty" , "Unsanitary" .)