Wind, more vicious across dunes, initially (7)
I believe the answer is:
meander
'wind' is the definition.
('meander' can be a synonym of 'wind')
'more vicious across dunes initially' is the wordplay.
'more vicious' becomes 'meaner' (I've seen this in other clues).
'across' indicates putting letters inside.
'initially' says to take the initial letters.
The initial letter of 'dunes' is 'd'.
'meaner' enclosing 'd' is 'MEANDER'.
(Other definitions for meander that I've seen before include "Wander aimlessly like a stream" , "Ramble about aimlessly" , "Wind about or wander here and there" , "Wander idly" , "Wind, bend" .)