Physicist at last uncovered huge gravitational force (3)
I believe the answer is:
tug
'gravitational force' is the definition.
(I've seen this before)
'physicist at last uncovered huge' is the wordplay.
'at last' suggests the final letters.
'uncovered' indicates the central letters.
The middle letters of 'huge' are 'ug'.
The last letter of 'physicist' is 't'.
't'+'ug'='TUG'
(Other definitions for tug that I've seen before include "Working boat" , "water tower" , "Sudden abrupt pull" , "Boat to pull larger one" , "Pull; loop on saddle" .)