Most convenient eastern development (7)
I believe the answer is:
nearest
'most convenient' is the definition.
(I've seen this in another clue)
'eastern development' is the wordplay.
'development' indicates an anagram.
'eastern' anagrammed gives 'NEAREST'.
(Other definitions for nearest that I've seen before include "Most imminent - most mean" , "With dearest, they're our loved ones" , "In greatest propinquity" , "Eastern (anag)" , "touching?" .)