Obtain through effort (4)
'obtain through effort' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for drum up that I've seen before include "Try to get (something) by canvassing" , "Attempt to get support by canvassing" , "Bring about (something) by constant and persistent effort" , "To attract" , "Attempt to obtain (support)" .)
(Other definitions for earn that I've seen before include "Be paid for work" , "Deserve; get paid" , "Merit (a reward)" , "Acquire by ones' effort" , "Deserve, gain" .)