Definitions
1.nounSound with a frequency greater than the upper limit of human hearing, which is approximately 20 kilohertz.
2.nounThe use of ultrasonic waves for diagnostic or therapeutic purposes.
3.nounA performer who understudies; a standby.
4.adjectiveUnusable; of no use.
5.adjectiveNot working (machinery, etc).
6.adjectiveImpractical.