Peevish with formal greeting showing arm (8)
I believe the answer is:
crossbow
This clue might be a double definition.
'peevish with formal greeting' is the first definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'arm' is the second definition.
(crossbow is a kind of arm)
'showing' is the link.
Can you help me to learn more?
(Other definitions for crossbow that I've seen before include "Ancient weapon, shot bolts" , "Old weapon wiht mechanism for firing bolt" , "Weapon firing bolts" , "Weapon (used to set off a quarrel?)" , "One responsible for shooting bolts" .)