In a trice
In a single moment, with no delay.
Trice is no longer a commonly used word but, by our understanding of our knowledge of the phrase 'in a trice' we can work easily out that it means 'a very short period of time'. The phrase is the only place we are now likely ever to come across the word. 'A short period of time' isn't the original meaning of 'trice' though - it had a more specific meaning, which was 'at a single pull'. This derived from the name given in the 14th century to a nautical windlass or pulley (variously 'tryse', 'tryce', 'trise' or 'trice') - hence the 'single pull' meaning.
The phrase was first recorded, in the 15th century, in the form 'at a trice'; for example, in the verse The lyfe of Ipomydon, 1440:
The howndis... Pluckid downe dere all at a tryse. [The hounds... plucked down deer all at a trice]
The first recording of the 'in a trice' version of the phrase is in John Skelton's Poetical Works, 1508:
To tell you what conceyte I had than in a tryce, The matter were to nyse.
See also: the meaning and origin of 'in a jiffy'.