SURDa.
[L. surdus, deaf.] Deaf; not having the sense of hearing. [Not used.]
1. Upheard. [Not used.]
2. Designating a quantity whose root cannot be exactly expressed in numbers.
SURDn.
In algebra, a quantity whose root cannot be exactly expressed in numbers. Thus 2 is a surd number, because there is no number which multiplied into itself, will exactly produce 2.