Strength of warning about Tesla (5)
I believe the answer is:
forte
'strength' is the definition.
(synonyms)
'warning about tesla' is the wordplay.
'warning' becomes 'fore' (used to warn of airborne balls on a golf course).
'about' means one lot of letters goes inside another.
'tesla' becomes 'T' (scientific unit).
'fore' going around 't' is 'FORTE'.
'of' is the link.
(Other definitions for forte that I've seen before include "Thing at which one excels" , "In music, to be played loudly" , "Skill" , "Strong point - loudly (in music)" , "Strength" .)