Opening verse put at the front by Roman poet (4)
I believe the answer is:
void
'opening' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for void that I've seen before include "Nullify" , "Null and empty" , "Empty space or vacuum" , "Not valid or legally binding" , "absence of a suit" .)