Small piece of gum or Sellotape (6)
I believe the answer is:
morsel
'small piece' is the definition.
(I've seen this before)
'of gum or sellotape' is the wordplay.
'of' says the answer is hidden in the clue.
'MORSEL' can be found hidden inside 'gum or sellotape'.
(Other definitions for morsel that I've seen before include "Titbit" , "a little food" , "A shred as of bread" , "Tasty little piece" , "Small amount of food, a bite" .)