Become large and roar (5)
I believe the answer is:
growl
'roar' is the definition.
(thesaurus)
'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' is the link.
(Other definitions for growl that I've seen before include "Noise of an angry dog" , "bare teeth" , "Grumble; roar" , "Low rumble" , "Sound like hostile or angry dog" .)