Big lizards alarming us again (7)
I believe the answer is:
iguanas
'big lizards' is the definition.
'iguanas' can be an answer for 'lizards' (iguana is a kind of lizard). I'm unsure of the 'big' bit.
'alarming us again' is the wordplay.
'us again' can be anagrammed to 'IGUANAS'.
Though, I'm not clear how this is indicated.
Can you help me to learn more?
(Other definitions for iguanas that I've seen before include "Large lizards" , "Asia gun (anag.)" , "Monitors" , "Tropical tree lizards" , "beasts" .)