Buoyancy aid (4,6)
'buoyancy aid' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for life jacket that I've seen before include "Flotation garment" , "Mae West" , "protective coat" , "Cover on biography" , "Buoyant belt" .)
(Other definitions for float that I've seen before include "Money in hand" , "Be buoyant" , "Drift aimlessly" , "Milk cart" , "Bob" .)