Omnium-gatherum is a grand term for a miscellaneous collection.
One of my reference books disparagingly calls it Dog Latin and it’s a fair description. The first part is genuine enough, being the genitive plural of omnis, all (omnibus, for what we prefer nowadays to call a bus, is the dative plural of the same word). The second part, however, is just the English word gather with a fake Latin ending. The 1788 second edition of Francis Grose’s Classical Dictionary of the Vulgar Tongue says it’s a “jocular imitation of law Latin” and this seems plausible.
There’s an older form, omnigatherum, mainly Scots, which the OED says was used from the seventeenth century for a group of craftsmen in Stirling, such as coopers, glassworkers, dyers, and gardeners, whose skills weren’t recognised in a formal trade guild but who were lumped together for some purposes, mostly taxation.
Omnium-gatherum has been known since the sixteenth century. In view of its bastard form, it’s odd that the first recorded user should have been the highly educated Greek scholar Richard Croke, in a letter to Thomas Cranmer in 1530.