Perfect, small principles (6)
I believe the answer is:
ideals
'principles' is the definition.
(I've seen this before)
'perfect small' is the wordplay.
'perfect' becomes 'ideal' ('ideal' can be similar in meaning to 'perfect').
'small' becomes 's' (abbreviation - e.g. clothes size).
'ideal'+'s'='IDEALS'
(Other definitions for ideals that I've seen before include "Models of excellance" , "Highest standards, model objectives" , "Models, exemplars" , "Bad ladies have high principles" , "'Perfect models, highest notions (6)'" .)