I’d never come across it until last night, when a program informed me it couldn’t rotate an image losslessly. It does, however, get 164,000 hits on Google, all of which seem at a cursory glance to refer to loss of data with reference to computer programs.
How long has this been around? The adverb doesn’t yet seem to have made it into the dictionaries, but ‘lossless’ is quite old: obsolete in the general sense (Milton used it), and alive according to the OED in the special sense of: ‘Characterized by or causing no dissipation of electrical or electromagnetic energy.’
Has anyone actually heard it used, as opposed to seeing it in print? Perhaps I just don’t know the right geeks, but I can’t imagine saying it instead of ‘without loss’ or ‘without losing data’. It isn’t really any shorter than the former, and you’d have to allow extra time for stumbling, or speaking deliberately slowly to ensure that you didn’t stumble over it. It’s my candidate for the most awkward word in the language, easily displacing all those -lily adverbs (heavenlily, lovelily and the like) that nobody ever says either.