Cations derived formally by attachment of one hydron to the nitrogen atom of a nitrile and hydrocarbyl derivatives thereof. E.g.
N04156.png benzonitrilium.
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1351 (https://doi.org/10.1351/pac199567081307)