Free publicity break (6)
I believe the answer is:
adrift
'free' is the definition.
(thesaurus)
'publicity break' is the wordplay.
'publicity' becomes 'ad' (advert).
'break' becomes 'rift' (I've seen this before).
'ad'+'rift'='ADRIFT'
(Other definitions for adrift that I've seen before include "like Mary Celeste?" , "not settled" , "No longer fixed in position" , "Floating uncontrolled" , "'Floating without direction, not tied up (6)'" .)