Vessel made from copper and phosphorus (3)
I believe the answer is:
cup
'vessel' is the definition.
(I know that Cup is a vessel)
'copper and phosphorus' is the wordplay.
'copper' becomes 'cu' (Cu is the chemical symbol for copper).
'and' means one lot of letters go next to another.
'phosphorus' becomes 'P' (P is the chemical symbol for phosphorus).
'cu'+'p'='CUP'
'made from' acts as a link.
(Other definitions for cup that I've seen before include "Beaker" , "Container to drink from - prize" , "Sort of cake" , "Trophy, drink" , "Chalice; trophy" .)