What is A Fortiori?

Legal Definition
"From stronger". An a fortiori argument is an "argument from a stronger reason", meaning that because one fact is true, that a second related and included fact must also be true.
Legal Definition
A Latin term meaning literally 'from [the] stronger'. Translated into English and used in the particular context of legal writing, the term often means 'from [the] stronger [argument]'. If a particular fact is true, then one can infer that a second fact is also true.
Legal Definition
Latin and means more effective or with greater reason.