Sir Isaac’s novel tone curtailed (6)
I believe the answer is:
newton
'sir isaac's' is the definition.
I can't tell whether this definition defines the answer.
'novel tone curtailed' is the wordplay.
'novel' becomes 'new' ('new' can be a synonym of 'novel'**).
'curtailed' means to remove the last letter.
'tone' with its last letter taken off is 'ton'.
'new'+'ton'='NEWTON'
Can you help me to learn more?
(Other definitions for newton that I've seen before include "Great English scientist who discovered gravity" , "Scientist formulating laws of motion" , "'English physicist, described the law of gravity (6)'" , "English mathematician and physicist, d. 1727" , "Isaac . . . . . ., great English physicist who discovered gravity" .)