Like a bird, by way of article outside (5)
I believe the answer is:
avian
'like a bird' is the definition.
(I've seen this in another clue)
'by way of article outside' is the wordplay.
'by way of' becomes 'via' (via means by way of or by means of).
'article' becomes 'an' (indefinite article).
'outside' indicates putting letters inside.
'via' inserted into 'an' is 'AVIAN'.
(Other definitions for avian that I've seen before include "Birdlike" , "Like rails, for example" , "Like a booby" , "To do with birds - like a dangerous flu" , "Lizard with adhesive foot-pads" .)