The pure rotational spectrum of the NiCN radical (X (2)Delta(i)) has been recorded using millimeter/sub-mm direct absorption techniques in the range 360-550 GHz. Transitions arising from four nickel isotopomers (Ni-58,Ni-60,Ni-62,Ni-64) and (NiCN)-Ni-58-C-13 were observed in the ground vibrational state, as well as lines originating in the v(2) bending and v(1) stretching modes. In the vibrational ground state, transitions from both spin-orbit components (Omega=5/2 and 3/2) were identified; in the Omega=3/2 ladder, significant lambda-doubling was observed. Multiple vibronic components were found for each bending quantum recorded, a result of Renner-Teller interactions. These components were only observed in the lower spin-orbit ladder (Omega=5/2), however, suggesting that spin-orbit coupling dominates the vibronic effects. The ground-state data were analyzed with a case (a) Hamiltonian, generating rotational, spin-orbit, and lambda-doubling constants for (NiCN)-Ni-58 and (NiCN)-Ni-60. The vibrationally excited lines were modeled with effective rotational parameters, except where a case (c) or case (b) coupling scheme could be meaningfully used. From the ground-state rotational parameters, r(0), r(s), and r(m)((1)) structures were derived as well. NiCN appears to be a covalently bonded molecule with similar properties to NiH. (C) 2003 American Institute of Physics.