One-sided version of a Latin rule (10)
I believe the answer is:
unilateral
'one-sided' is the definition.
(I know that one-sided can be written as unilateral)
'version of a latin rule' is the wordplay.
'version of' indicates an anagram.
'a'+'latin'+'rule'='alatinrule'
'alatinrule' anagrammed gives 'UNILATERAL'.
(Other definitions for unilateral that I've seen before include "Done only by one side" , "One-sided" , "affecting only one person out of several" .)