Green leader beginning to make waves (7)
I believe the answer is:
emerald
'green' is the definition.
(I know that emerald is a type of green)
'leader beginning to make waves' is the wordplay.
'beginning to' suggests taking the first letters.
'waves' indicates anagramming the letters.
The initial letter of 'make' is 'm'.
'leader'+'m'='leaderm'
'leaderm' is an anagram of 'EMERALD'.
(Other definitions for emerald that I've seen before include "and 1 Across: Ireland" , "a type employed by the press" , "Green like this isle" , "Precious green stone" , "Gem; type of moth" .)