New recruit that is taken from castle (4)
I believe the answer is:
rook
'castle' is the definition.
(thesaurus)
'new recruit that is taken' is the wordplay.
'new recruit' becomes 'rookie' (I've seen this before).
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'taken' suggests deleting specific letters.
'rookie' with 'ie' taken away is 'ROOK'.
'from' acts as a link.
(Other definitions for rook that I've seen before include "Gregarious crow" , "Rip off - bird" , "man in marginalised position, initially" , "Defraud; bird; chessman" , "Use deceit to get money" .)