Definition of "unpronounceable"

A Hungarian baron, with an unpronounceable name, had that very morning been so struck with Lady Penrhyn's beauty, that, not knowing she was married, he laid himself, castle, sabre, and fur pelisses at her feet, for immediate acceptance.

1838 (date written), L[etitia] E[lizabeth] L[andon], chapter XIII, in Lady Anne Granard; or, Keeping up Appearances. […], volume I, London: Henry Colburn, […], published 1842, page 166

In many ways, the salarian political network functions like the noble families of Earth's Medieval Europe. Structurally the government consists of fiefdoms, baronies, duchies, planets, and marches (colonization clusters). These are human nicknames; the original salarian is unpronounceable.

2008, BioWare, Mass Effect, Redwood City: Electronic Arts, PC, scene: Salarians: Government Codex entry

Synthetic fragrances can contain a laundry list of chemicals — hormone disrupters, petroleum-derived unpronounceables, asthma triggers and on and on.

2009 March 13, “Natural Selection”, in New York Times‎

Finally, if there are some “unpronounceables” in the list, ensure that they are minimal and not artificial anything—artificial colors, preservatives, flavors, or sweeteners.

2010, Deanna M. Minich, An A-Z Guide to Food Additives