Host is daft, ignoring bishop (4)
I believe the answer is:
army
'host' is the definition.
(thesaurus)
'daft ignoring bishop' is the wordplay.
'daft' becomes 'barmy' ('barmy' can be a synonym of 'daft').
'ignoring' suggests deleting specific letters.
'bishop' becomes 'b' (abbreviation used in chess).
'barmy' with 'b' removed is 'ARMY'.
'is' is the link.
(Other definitions for army that I've seen before include "A great number (of soldiers?)" , "Organisation for soldiering" , "Fighting unit" , "Multitude" , "Fighting force" .)