Insensitive union, no emotion
I believe the answer is:
unfeeling
'insensitive' is the definition.
(similar in meaning)
'union no emotion' is the wordplay.
'union' becomes 'U' (common abbreviation as in 'Trades Union Congress').
'no' becomes 'n' (common abbreviation).
'emotion' becomes 'feeling' (I've seen this before).
'u'+'n'+'feeling'='UNFEELING'
(Other definitions for unfeeling that I've seen before include "Heartless" , "Hard-hearted" , "Callous" , "Lacking in sympathy or emotion" .)