Guest called in endlessly demanding (8)
I believe the answer is:
stranger
'guest' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'called in endlessly demanding' is the wordplay.
'called' becomes 'rang' (called on the phone).
'in' is an insertion indicator.
'endlessly' means to remove the last letter.
'demanding' becomes 'stern' (demanding can mean stern or strict).
'stern' with its final letter removed is 'ster'.
'rang' going into 'ster' is 'STRANGER'.
Can you help me to learn more?
(Other definitions for stranger that I've seen before include "Odder, more peculiar" , "Truth can be ... than fiction" , "unfamiliar figure" , "One who is little known" , "Less familiar" .)