It encourages laying in a little money (4,3)
I believe the answer is:
'a little money' is the definition.
'nest egg' can be an answer for 'money' (nest egg is a kind of money). I am not sure about the 'a little' bit.
'it encourages laying in' is the wordplay.
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'encourages' becomes 'nes' (I am not sure about this - if you are sure you should believe this answer much more).
'laying' becomes 'egg laying' (synonyms).
'in' is an insertion indicator.
't' inserted within 'nesegg' is 'NEST-EGG'.
Can you help me to learn more?
(Other definitions for nest egg that I've seen before include "Sum saved for the future" , "A saving for the future - by bird?" , "Money set aside for retirement" , "money put away" , "Is it to encourage laying" .)