Poster on gulf, floating away (6)
I believe the answer is:
adrift
'floating away' is the definition.
'adrift' can be an answer for 'floating' (thesaurus). I'm unsure of the 'away' bit.
'poster on gulf' is the wordplay.
'poster' becomes 'ad' (short for advert).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'gulf' becomes 'rift' (I've seen this in another clue).
'ad'+'rift'='ADRIFT'
Can you help me to learn more?
(Other definitions for adrift that I've seen before include "Floating uncontrolled" , "cut loose" , "Afloat without steerage" , "Aimlessly floating" , "Afloat without control" .)