Promote development of giant site (9)
I believe the answer is:
instigate
'promote' is the definition.
(to instigate is to promote or provoke)
'development of giant site' is the wordplay.
'development of' indicates anagramming the letters (letters developed in another way).
'giant'+'site'='giantsite'
'giantsite' is an anagram of 'INSTIGATE'.
(Other definitions for instigate that I've seen before include "Urge and bring about" , "I taste gin to incite or urge" , "I get saint to urge or incite" , "Start" , "Provoke" .)