Repeat base expression of Scotsman dropping ball (4)
I believe the answer is:
echo
'repeat' is the definition.
(synonyms)
'base expression of scotsman dropping ball' is the wordplay.
I cannot really understand how this works, but
'base' could be 'e' (Euler's number - base of natural logarithms) and 'e' is present in the answer.
'of' could be 'o' and 'o' is found in the answer.
The remaining letters 'ch' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for echo that I've seen before include "Radio operator's word for 'E'" , "The distant sound" , "repercussion" , "Response" , "Before foxtrot" .)