Opposition leader's share in speech (7)
I believe the answer is:
oration
'speech' is the definition.
(oration is a kind of speech)
'opposition leader's share' is the wordplay.
'leader' says to take the initial letters.
'share' becomes 'ration' (a ration is a share of a limited resource).
The first letter of 'opposition' is 'o'.
'o'+'ration'='ORATION'
'in' acts as a link.
(Other definitions for oration that I've seen before include "Making a speech" , "A formal or public speech" , "words" , "A formal or ceremonial speech" , "Address" .)