Snake is more annoyed without a head (5)
I believe the answer is:
adder
'snake' is the definition.
(I know that adder is a type of viper)
'more annoyed without a head' is the wordplay.
'more' becomes 'm'.
'annoyed' becomes 'mad' (mad can mean annoyed or angered).
'without' indicates named letters should be taken away.
'a head' becomes 'der' (I can't justify this - if you can you should believe this answer much more).
'mad' with 'm' taken out is 'ad'.
'ad'+'der'='ADDER'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for adder that I've seen before include "Venemous snake" , "poisoner" , "venomous creature" , "Viper common in northern Eurasia" , "Sliding" .)