One creche assembled union (9)
I believe the answer is:
coherence
'union' is the definition.
(coherence is a kind of union)
'one creche assembled' is the wordplay.
'assembled' indicates an anagram.
'one'+'creche'='onecreche'
'onecreche' is an anagram of 'COHERENCE'.
(Other definitions for coherence that I've seen before include "Logical consistency" , "Sticking together" , "union" , "sense of unity" , "ability to talk sense" .)