Bring about or start up, just in case (5)
I believe the answer is:
cause
This could be a double definition.
'bring about' is the first definition.
(I've seen this before)
'start up just in case' is the second definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'or' acts as a link.
Can you help me to learn more?
(Other definitions for cause that I've seen before include "Grounds" , "Produce (an effect)" , "Reason; belief" , "Make happen; something deserving support" , "Bring about" .)