[′mäd·ə‚fīd ′häŋk·əl ‚fəŋk·shənz] (mathematics) The functions defined by Kv(x) = (i π/2) exp (iv π/2) Hv(1)(ix), where Hv(1)is the first Hankel function of order v, and x is real and positive. Also known as modified Bessel function of the second kind.