The least difficult that is initially set in one direction (7)
I believe the answer is:
easiest
'the least difficult' is the definition.
('easy' is the opposite of 'difficult' so 'easiest' should be a synonym for 'least difficult')
'that is initially set in one direction' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'initially' suggests taking the first letters.
'in' is an insertion indicator.
'one direction' becomes 'east' (compass direction).
The initial letter of 'set' is 's'.
'ie'+'s'='ies'
'ies' put inside 'east' is 'EASIEST'.
(Other definitions for easiest that I've seen before include "most like pie" , "Most simple" , "Most comfortable" , "Requiring the least amount of effort" , "Least difficult" .)