Measure of importance under the mistletoe? (7,5)
I believe the answer is:
pecking order
'mistletoe?' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'measure of importance under' is the wordplay.
I cannot really understand how this works, but
'measure' could be 'peck' (peck is a kind of measure) and 'peck' is located in the answer.
'of' could be 'o' and 'o' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'the' acts as a link.
(Other definitions for pecking order that I've seen before include "Animal Farm hierarchy" , "Hierarchy (of hens?)" , "Gradation" .)