Result from Foreign Dictionaries (2 entries found)
From The Collaborative International Dictionary of English v.0.48 [gcide]:
A fortiori \A for`ti*o"ri\ [L.] (Logic & Math.)
With stronger reason.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
a fortiori
adv 1: with greater reason; for a still stronger, more certain
reason; "if you are wrong then, a fortiori, so am I"