Lethal (5)
(Other definitions for final that I've seen before include "binding" , "Last match in a competition" , "Last in a series of games or contests" , "Not to be altered" , "big match" .)
'lethal' is the definition.
(similar in meaning)
This is the entire clue.
(Other definitions for fatal that I've seen before include "Unavoidable" , "making one late" , "Calamitous" , "Leading to disaster" , "Bringing ruin" .)
'lethal' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for toxic that I've seen before include "word describing bad things" , "Harmful - cox it (anag)" , "Deadly - venomous" , "Poisonous, noxious" .)
'lethal' is the definition.
(I know that lethal can be written as deadly)
This is all the clue.
(Other definitions for deadly that I've seen before include "No small bore" , "Belladonna" , "Lethal, capable of causing fatality" , "sniper aspires to be" , "There are seven such sins" .)