Vicious horn protects one (5)
I believe the answer is:
rhino
'vicious horn protects one' is the definition.
I can't judge whether this defines the answer.
'vicious horn protects one' is the wordplay.
'vicious' is an anagram indicator.
'protects' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'horn' is an anagram of 'rhno'.
'rhno' placed around 'i' is 'RHINO'.
Can you help me to learn more?
(Other definitions for rhino that I've seen before include "The necessary" , "greens" , "Funds" , "one might charge in Africa" , "Large animal with a horn on its snout, in short" .)