Ever-changing small swerves (5)
I believe the answer is:
veers
'swerves' is the definition.
('veer' can be a synonym of 'swerve')
'ever-changing small' is the wordplay.
'changing' indicates anagramming the letters.
'small' becomes 's' (abbreviation - e.g. clothes size).
'ever' is an anagram of 'veer'.
'veer'+'s'='VEERS'
(Other definitions for veers that I've seen before include "Turns sharply" , "Swerves" , "Changes direction abruptly" .)