Big lizards alarming us again (7)
I believe the answer is:
'big lizards' is the definition.
'iguanas' can be an answer for 'lizards' (iguana is a kind of lizard). I'm not certain of the 'big' bit.
'alarming us again' is the wordplay.
'us again' anagrams to 'IGUANAS'.
Though, I am not sure 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" .)