Pig and tailless wild dog getting on (8)
I believe the answer is:
boarding
'getting on' is the definition.
('board' can be a synonym of 'get on')
'pig and tailless wild dog' is the wordplay.
'pig' becomes 'boar' (male pig).
'and' is a charade indicator (letters next to each other).
'tailless' means to remove the last letter (the tail of the word is removed).
'wild dog' becomes 'dingo' (dingo is a kind of wild dog).
'dingo' with its last letter taken away is 'ding'.
'boar'+'ding'='BOARDING'
(Other definitions for boarding that I've seen before include "public school arrangement" , "Staying at school" , "Living at school" , "Sort of party" , "Getting on (a train)" .)