Tono- is a prefix that means "tone" or "tension". It's often used in medical terminology to describe a condition related to the tone or tension of muscles or other tissues.
For example:
* Tonometry is the measurement of intraocular pressure (the pressure inside the eye).
* Hypotonia is a condition of low muscle tone.
* Hypertonia is a condition of high muscle tone.
It's important to note that "tonous" is not a standard word in English. It is likely a variant spelling of "tonus", which refers to the state of normal tension in muscles.