Crossword Genius

Riot if road is cut short and relaid? Even more certain (1,8)

Ross

I believe the answer is:

a fortiori

I'm a little stuck... Click here to teach me more about this clue!

'road is cut short and relaid? even more certain' is the definition.
I can't judge whether this definition defines the answer.

'riot' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'riot' is 'orti' which is within the answer.
This may be the basis of clue (or it may be nonsense).

'if' acts as a link.

Can you help me to learn more?

(Other definitions for a fortiori that I've seen before include "with greater reason" , "By inference, even more" , "Latin phrase: With even stronger reason than that already accepted" , "more conclusively" , "with better grounds" .)

I've seen this clue in The Hindu.
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