Veer erratically as always (4)
I believe the answer is:
ever
'as always' is the definition.
(I've seen this before)
'veer erratically' is the wordplay.
'erratically' is an anagram indicator.
'veer' anagrammed gives 'EVER'.
(Other definitions for ever that I've seen before include "To the end of time" , "Eternally" , "Always, at any time" , "constantly" , "Eternity" .)