Believe everyone to have portmanteau (7)
I believe the answer is:
holdall
'have portmanteau' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'believe everyone' is the wordplay.
'believe' becomes 'hold' (synonyms).
'everyone' becomes 'all' (all people).
'hold'+'all'='HOLDALL'
'to' is the link.
Can you help me to learn more?
(Other definitions for holdall that I've seen before include "Large case, with handles" , "Large bag (no need for another?)" , "Big bag" , "Largish bag" , "Large carrying bag" .)