malapropism (n.)

"act or habit of misapplying words through ambition to use fine language," also a word so misapplied, 1826, from Mrs. Malaprop, character in Sheridan's play "The Rivals" (1775), noted for her ridiculous misuse of large words (such as contagious countries for contiguous countries), her name coined from malapropos.

When Mrs. Malaprop, in Sheridan's Rivals, is said to 'deck her dull chat with hard words which she don't understand,' she protests, 'Sure, if I reprehend anything in this world it is the use of my oracular tongue, & a nice derangement of epitaphs'—having vague memories of apprehend, vernacular, arrangement, & epithets. She is now the matron saint of those who go wordfowling with a blunderbuss. [Fowler]