According to NASA, a spectral radiometer is a multispectral sensor.
Spectroradiometer—A radiometer that measures the intensity of radiation in multiple wavelength bands (i.e., multispectral). Many times the bands are of high-spectral resolution, designed for remotely sensing specific geophysical parameters
Perhaps you're thinking of a spectrometer, which is slightly different, but similar
Spectrometer—A device that is designed to detect, measure, and analyze the spectral content of incident electromagnetic radiation. Conventional imaging spectrometers use gratings or prisms to disperse the radiation for spectral discrimination.
For the sake of being thorough,
Radiometer—An instrument that quantitatively measures the intensity of electromagnetic radiation in some bands within the spectrum. Usually, a radiometer is further identified by the portion of the spectrum it covers; for example, visible, infrared, or microwave.
Hyperspectral radiometer—An advanced multispectral sensor that detects hundreds of very narrow spectral bands throughout the visible, near-infrared, and mid-infrared portions of the electromagnetic spectrum. This sensor’s very high spectral resolution facilitates fine discrimination between different targets based on their spectral response in each of the narrow bands.
MODIS has an imaging spectroradiometer that measures 36 bands. Bands 1-19 are relatively wide, and imagery from these bands is considered multispectral. Bands 20-36 are much more fine, covering a nearly continuous spectral range, resulting in hyperspectral imagery.
The Operational Land Imager (OLI) on Landsat 8 is also a multispectral sensor.