Green’s Dictionary of Slang

1. an act of violence, a beating.

1999		J. Cameron Brown Bread in Wengen [ebook] ‘Serious mash-up bring down heavy grief on your hoo-ha innit?’.
2004		(con. 1960s-70s) T. Taylor Top Fellas 15/1: By the early sixties the mod ranks welled with lively lads who liked nothing better than a mash-up.

2. a song that is a mix of two completely different songs spliced into one; ext. use to other popular things.

2002		N.Y. Times 9 May n.p.: The songs, called mash-ups or bootlegs, typically match the rhythm, melody and underlying spirit of the instrumentals of one song with the a cappella vocals of another. And the more odd the pairing the better.
2004		Guardian 15 Aug. 🌐 Parkspliced...Witness the second coming with this triumphant collaboration of remixes and mash-ups of every track on the epoch-defining Parklife from the denizens of the mighty GYBO messageboard.
2009		Observer Mag. 4 Jan. 24: Spiz’ike is the name of a limited-edition trainer – a mash-up of several early styles of Air Jordan.
2017		S. Bythell Diary of a Bookseller 275: [D]id we upset the neighbors last night with our ‘End of Year’ Book Shop mash-up of hip-hop & swing dance moves .
2023		J. Jackson Pineapple Street 105: [A] place that felt like an expensive mash-up of Antiques Roadshow and Hoarders.