Plump old lady embracing current model (7)
I believe the answer is:
optimum
'model' is the definition.
(I've seen this before)
'plump old lady embracing current' is the wordplay.
'plump' becomes 'opt' (I've seen this before).
'old lady' becomes 'mum' (I've seen this before).
'embracing' means one lot of letters goes inside another.
'current' becomes 'i' (symbol for electric current).
'opt'+'mum'='optmum'
'optmum' enclosing 'i' is 'OPTIMUM'.
(Other definitions for optimum that I've seen before include "Most favourable point" , "Most favourable amount" , "Best, most favourable" , "Best (result)" , "The best possible" .)