In the car, ideally, it's dry (4)
I believe the answer is:
arid
'dry' is the definition.
(similar in meaning)
'in the car ideally it's' is the wordplay.
'in' indicates a hidden word.
'ARID' is hidden in the letters of 'car ideally ts'.
(Other definitions for arid that I've seen before include "(Of land) very dry" , "Dry, devoid of interest" , "Excessively dry" , "water shortage?" , "Without much rainfall" .)