Pipsqueak should save money - that's basic (8)
I believe the answer is:
rudiment
'basic' is the definition.
(I've seen this before)
'pipsqueak should save money' is the wordplay.
I cannot really see how this works, but
'money' could be 'dime' and 'dime' is found in the answer.
'pipsqueak' could be 'runt' (I've seen this in another clue) and 'runt' is found in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for rudiment that I've seen before include "Basic form of something" , "First principle" , "Beginning" , "Fundamental principle" , "Basic principle" .)