Fish cake beneath tray for starter? (5)
I believe the answer is:
troll
'fish' is the definition.
(trolling is a type of fishing)
'cake beneath tray for starter?' is the wordplay.
'cake' becomes 'roll' (roll is a type of cake eg Swiss roll).
'beneath' says to put letters next to each other (in a down clue, some letters go beneath others).
'for starter?' says to take the initial letters (I've seen 'for starters' mean this).
The initial letter of 'tray' is 't'.
'roll' put after 't' is 'TROLL'.
(Other definitions for troll that I've seen before include "Draw baited line, to lure fish" , "online commenter" , "cyber-bully" , "Dwarf (or giant) of Norse myth" , "Ugly Norse dwarf" .)