Reduced in size, said of an interval contracted within its natural space or compass by the application of a sharp or natural to the lower tone, or of a flat or natural to the upper tone.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (adjective) (adj.) (adjective)

Usage examples:

It appeared to me that their numbers were diminished
- Adventures in the Far West by W.H.G. Kingston
The firing diminished and stopped.
- Waiting for Daylight by Henry Major Tomlinson
If a woman gives birth to a boy and a girl, ill luck will enter the land, the land will be diminished
- Babylonian-Assyrian Birth-Omens and Their Cultural Significance by Morris Jastrow