Judge about to imprison hard solicitor's client (4)
I believe the answer is:
john
'solicitor's client' is the definition.
(client of a sex worker - someone who 'solicits')
'judge about to imprison hard' is the wordplay.
'judge' becomes 'j' (abbreviation for judge).
'about' becomes 'on' (as in a book 'on' a certain topic).
'to imprison' means one lot of letters goes inside another.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'on' going around 'h' is 'ohn'.
'j'+'ohn'='JOHN'
(Other definitions for john that I've seen before include "Matthew, Mark, Luke and . . . ." , "With nineteen accross twentieth century US actor known for westerns, etc" , "From Gwen" , "Head" , "Old King" .)