Imagine mother taking religious lessons! (5)
I believe the answer is:
dream
'imagine' is the definition.
(dreaming is a kind of imagining)
'mother taking religious lessons' is the wordplay.
'mother' becomes 'dam' (female parent of an animal).
'taking' indicates putting letters inside.
'religious lessons' becomes 're' (Religious Education. I am not sure about the 'religious' bit.).
'dam' enclosing 're' is 'DREAM'.
Can you help me to learn more?
(Other definitions for dream that I've seen before include "Vision - very pleasant person" , "Fantasy; imagine" , "dozy state" , "Night-time fantasy" , "Somniate" .)