Imagine the mother is ringing about (5)
I believe the answer is:
dream
'imagine' is the definition.
(dreaming is a kind of imagining)
'mother is ringing about' is the wordplay.
'mother' becomes 'dam' (female parent of an animal).
'is ringing' means one lot of letters goes inside another.
'about' becomes 're' ('re' means regarding or about).
'dam' placed around 're' is 'DREAM'.
'the' is the link.
(Other definitions for dream that I've seen before include "Illusion" , "Fancy (usually 7)" , "Armed (anag)" , "person to good to be true" , "Perfect" .)