Sun bear: unstable potential killer (5)

I believe the answer is:

sabre

I'm a little stuck... Click here to teach me more about this clue!

'potential killer' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'sun bear unstable' is the wordplay.
'sun' becomes 's' (abbreviation).
'unstable' indicates anagramming the letters.
'bear' is an anagram of 'abre'.
's'+'abre'='SABRE'

Can you help me to learn more?

(Other definitions for sabre that I've seen before include "Sword (that may be rattled)" , "Slasher" , "Type of sword" , "Large wasp" , "Bares (anag.)" .)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.