Monotimbral (from the root prefix mono meaning one, and timbre meaning a specific tone of a sound independent of its pitch) is usually used in reference to electronic synthesizers which can produce a single timbre at a given pitch when pressing one key (if the synth is monophonic) or multiple keys (if the synth is polyphonic).
An electronic musical instrument may be multitimbral, which means it can produce two or more timbres (also called sounds or patches) at the same time. Instruments which may be multitimbral include synthesizers, samplers, and music workstations. A multitimbral instrument might be configurable in a variety of ways: