Fast movers by morning found at sea (6)
I believe the answer is:
jetsam
'found at sea' is the definition.
(I've seen this before)
'fast movers by morning' is the wordplay.
'fast movers by' becomes 'jets' (I can't explain this - if you can you should believe this answer much more).
'morning' becomes 'am' (as in je:00 AM).
'jets'+'am'='JETSAM'
Can you help me to learn more?
(Other definitions for jetsam that I've seen before include "Goods thrown overboard from ship in distress" , "Floating wreckage" , "Stuff cast overboard" , "lost cargo" , "Material flung overboard" .)