Become large and emit a threatening noise (5)
I believe the answer is:
growl
'emit a threatening noise' is the definition.
'growl' can be an answer for 'emit' (growling is a kind of emiting). I'm not sure about the 'a threatening noise' bit.
'become large' is the wordplay.
'become' becomes 'grow' (I've seen this in another clue).
'large' becomes 'L' (eg in clothes sizes).
'grow'+'l'='GROWL'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for growl that I've seen before include "snap" , "Low rumble" , "Show aggression as boxer" , "Dull, rumbling sound of an animal" , "Threatening dog's noise" .)