Perhaps tape large creature next to tiny one (7)
I believe the answer is:
sealant
'perhaps tape' is the definition.
(tape may be used to seal something up)
'large creature next to tiny one' is the wordplay.
'large creature' becomes 'seal' (type of animal. I am not sure about the 'large' bit.).
'next to' means one lot of letters go next to another.
'tiny one' becomes 'ant' (a tiny insect).
'seal'+'ant'='SEALANT'
(Other definitions for sealant that I've seen before include "Substance filling gap to prevent leakage" , "Eg, Fermat or Napier" , "Material to stop leaks" , "Material blocking leaks" , "Filler used to close a gap" .)