Current agreement's the last word (5)
I believe the answer is:
ideal
'the last word' is the definition.
('the last word in something' is its ideal version)
'current agreement's' is the wordplay.
'current' becomes 'I' (symbol for electric current).
'agreement' becomes 'deal' (deal is a kind of agreement).
'i'+'deal'='IDEAL'
(Other definitions for ideal that I've seen before include "fanciful" , "Just the ticket" , "Exemplar" , "faultless" , "In her dreams" .)