Several people have emailed me asking where bated breath comes from. Bate is a verb dating to the beginning of the14th century meaning to deprive or to lessen; it is a clipped form of abate.
Shakespeare was the first writer we know of to use bated breath, in 1596 in The Merchant of Venice, I.iii.125:
With bated breath, and whispring humblenesse.
Like most of Shakespeare's alleged coinages, this is probably not an invention of the Bard's; his use has simply survived while the writings of earlier and lesser writers have perished.
The term is commonly misspelled as baited breath.
(Source: Oxford English Dictionary, 2nd Edition)