Finishes on the call; misses deadline otherwise (4)

I believe the answer is:
else
'otherwise' is the definition.
(synonyms)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for else that I've seen before include "Besides, otherwise" , "Alternatively" , "Eels (anag)" , "In addition; different" , "Besides; instead" .)
