Take our cash over time? That's tough! (6)
I believe the answer is:
robust
'tough' is the definition.
(robust means tough or strong)
'take our cash over time?' is the wordplay.
I cannot quite see how this works, but
'take' could be 'rob' (I've seen this in another clue) and 'rob' is found in the answer.
'time?' could be 't' (abbreviation) and 't' is present in the answer.
The remaining letters 'us' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'that's' is the link.
Can you help me to learn more?
(Other definitions for robust that I've seen before include "Sturdy, resilient" , "Vigorous and hearty" , "Strong and vigorous" , "Sturdy and hardy" , "Strong and sturdy" .)