Sn (3)
I believe the answer is:
tin
'sn' is the definition.
(synonyms)
This is all the clue.
(Other definitions for tin that I've seen before include "Silvery metallic element" , "Metal element" , "A silvery-white metal often in cans" , "Silver-white element often used in food containers" , "1 down, symbol Sn" .)