So the bus is empty? (4)
I believe the answer is:
thus
'so' is the definition.
(I know that so can be written as thus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for thus that I've seen before include "'So, therefore (4)'" , "as indicated" , "Therefore, hence" , "Like so" , "an original Christmas gift" .)