Hide whenever in California (7)
I believe the answer is:
conceal
'hide' is the definition.
(synonyms)
'whenever in california' is the wordplay.
'whenever' becomes 'once' (I've seen this in another clue).
'in' is an insertion indicator.
'california' becomes 'cal' (short for California).
'once' inserted into 'cal' is 'CONCEAL'.
(Other definitions for conceal that I've seen before include "'Hide, keep secret (7)'" , "Hide, cover" , "Keep out of sight" , "Screen" , "hush up!" .)