Sibling has run out? Damn! (6)
I believe the answer is:
bother
'damn' is the definition.
(both are expressions of annoyance)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for bother that I've seen before include "Discommode, annoy" , "Irritate - concern oneself" , "Fuss and irritant" , "Badger" , "Annoy or pester" .)