RhymeZone: ultrashort definitions

Definitions of ultrashort:

adjective: Very short.
adjective: (sciences) Extremely short in duration, typically on the femtosecond scale
adjective: (physics, of a wave) Having a wavelength of between 1 and 10 metres
adjective: (finance) Having a very short term of investment, typically less than a year
noun: (finance) A bond with an extremely short term, typically less than a year

(Definitions from Wiktionary)