Countless milkmaids initially backing their workplace (6)
I believe the answer is:
myriad
'countless' is the definition.
(I know that countless can be written as myriad)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for myriad that I've seen before include "Host" , "A great number" , "Large indefinite number" , "Too numerous to be counted" , "Many" .)