Active article expelled by aerosol (4)
I believe the answer is:
spry
'active' is the definition.
(similar in meaning)
'article expelled by aerosol' is the wordplay.
'article' becomes 'a' (the indefinite article in English).
'expelled by' indicates named letters should be taken away.
'aerosol' becomes 'spray' (I've seen this before).
'spray' with 'a' taken away is 'SPRY'.
(Other definitions for spry that I've seen before include "Nimble, brisk" , "Sprightly" , "Light on one's feet" , "Quick and agile" , "Fleet" .)