Yale is developing without difficulty (6)
I believe the answer is:
easily
'without difficulty' is the definition.
('easily' can be a synonym of 'without difficulty')
'yale is developing' is the wordplay.
'developing' indicates anagramming the letters.
'yale'+'is'='yaleis'
'yaleis' is an anagram of 'EASILY'.
(Other definitions for easily that I've seen before include "Simply" , "Very probably" , "Without much difficulty" , "Effortlessly" , "With little difficulty" .)