Trained bear helping to show eccentricity (10)
I believe the answer is:
aberration
'eccentricity' is the definition.
(I've seen this in another clue)
'trained bear helping' is the wordplay.
'trained' indicates anagramming the letters (to train can mean to grow something into a shape).
'helping' becomes 'ration' (a ration is a serving or helping).
'bear' is an anagram of 'aber'.
'aber'+'ration'='ABERRATION'
'to show' is the link.
(Other definitions for aberration that I've seen before include "irregularity" , "Slip" , "Anomaly -- a Breton air (anag)" , "Deviation from normality" , "Straying" .)