As far as I know, though "surd" is said to derive from the Latin word "surdus", there is a little problem concernig its use in Mathematics. "Surdus" is a medioeval Latin word, it does not come from the classical or ancient Latin, while absurd exists since Romans. Why some numbers are called "blind" or "deaf"(the meanings of "surdus")? There was an error of translation from arabic: when European mathematicians face their Arab colleagues using the term
jadr, they traduced it as "deaf" or "blind", because in Arabic that word is used for both those handicaps, and in Latin the equivalent was "surdus". But they forgot - or did not know - that Arabic word has also another meaning: "bizarre", "strange", "uncommon"
1, while in Latin those further meanings are not of "surdus". The time passed and the term survived.