Drastic cut by base (6)
I believe the answer is:
severe
'drastic' is the definition.
(I've seen this before)
'cut by base' is the wordplay.
'cut' becomes 'sever' (severing is a kind of cutting).
'by base' becomes 'e' (I've seen this in other clues. I am not sure about the 'by' bit.).
'sever'+'e'='SEVERE'
Can you help me to learn more?
(Other definitions for severe that I've seen before include "Strict, hard" , "Sharp" , "Formal - unsmiling" , "Harsh and unbending" , "Taxing" .)