Fundamental work in recent decades on a variety of related topics can still leave one uncertain what individual documents mean by ‘organum’, particularly those prepared by clerks unversed in musical vocabulary. This essay looks at several types of document to ask whether they mean an organ, a siren, a wind instrument, a tool, a book, a gospel, or even Mass and Office. Paradoxically, the more ‘versatile’ the word, the likelier that organs were familiar.