UNPRONOUNCEABLE
unpronounceable, unutterable
(adjective) very difficult to pronounce correctly; “an unpronounceable foreign word”; “unutterable consonant clusters”
unpronounceable
(adjective) impossible or difficult to pronounce correctly
Source: WordNet® 3.1
Etymology
Adjective
unpronounceable (comparative more unpronounceable, superlative most unpronounceable)
Impossible or difficult to pronounce or articulate.
Noun
unpronounceable (plural unpronounceables)
Something difficult or impossible to pronounce.
Source: Wiktionary