Float in delta towards crevice (5)
I believe the answer is:
drift
'float' is the definition.
(synonyms)
'delta towards crevice' is the wordplay.
'delta' becomes 'd' (phonetic alphabet: alpha, bravo, charlie etc.).
'towards' means one lot of letters go next to another (I've seen this in other clues).
'crevice' becomes 'rift' (rift is a kind of crevice).
'd'+'rift'='DRIFT'
'in' is the link.
(Other definitions for drift that I've seen before include "Tendency" , "Go with the flow" , "Move with the current" , "Coast" , "Meander aimlessly" .)