Strange thing -- member of parliament is one who delays retirement (5,3)
I believe the answer is:
night owl
'one who delays retirement' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'strange thing member of parliament' is the wordplay.
'strange' indicates anagramming the letters.
'member of parliament' becomes 'owl' ('parliament' is the collective noun for 'owl').
'thing' with letters rearranged gives 'night'.
'night'+'owl'='NIGHT-OWL'
'is' is the link.
Can you help me to learn more?
(Other definitions for night owl that I've seen before include "One stays up late" , "Person who likes to be active late in the day" , "Nocturnal human (with a bird)" , "One active after dark" , "One who puts off retirement" .)