Needle Ten News to report only one side of the triangle (10)
I believe the answer is:
hypotenuse
'report only one side of the triangle' is the definition.
I can't judge whether this definition defines the answer.
'needle ten news' is the wordplay.
'needle' becomes 'hypo' (I have seen 'Sharp needle ' mean 'hypo' so perhaps 'needle' could also mean 'hypo').
'news' becomes 'use' (I am not sure about this - if you are sure you should believe this answer much more).
'hypo'+'ten'+'use'='HYPOTENUSE'
'to' is the link.
Can you help me to learn more?
(Other definitions for hypotenuse that I've seen before include "Side opposite right angle" , "long line" , "Longest side of right-angled triangle" , "Long side of right-angled triangle" , "Right-angled triangle's longest side" .)