Supports the truth of something (8)
I believe the answer is:
confirms
'supports the truth of something' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for confirms that I've seen before include "Supports the truth of something" , "Corroborates" , "Provides supporting evidence of the truth" , "Provides support for the truth of" , "Finalises or makes definite" .)