Malaphor is not a word yet but it’s a useful term that may yet get there. The term itself is a portmanteau — a word combined from parts of two other words — of malapropism and metaphor. Lawrence Harrison coined malaphor, back in August of 1976, in a Op Ed piece in the Washington Post. Harrison’s article isn’t readily available so I’m not sure exactly what he said, but most people writing about malaphors define the term as a mixed metaphor as, for example, “let’s burn that bridge when we come to it” combines “don’t burn your bridges” with “let’s cross that bridge when we come to it.” It seems to me that we already have “mixed metaphor” to describe that kind of mashup, but if we define a malaphor as a screwed-up metaphor, then a mixed metaphor would just be one type.
A malapropism is the use of a mistaken word that bears some resemblance to the correct one, usually to comic effect. A malapropism is not quite an eggcorn, which is a wrong word that sounds the same or almost the same as the word it replaces). It comes from Richard Sheridan’s 1775 play, “The Rivals,” in which a character, Mrs. Malaprop, is prone to fairly hilarious errors, like saying someone is “the very pineapple of politeness” or “as headstrong as an allegory on the banks of the Nile.” As @Guy_in_PEI pointed out, Sheridan named the character for the French phrase mal à propos, meaning inappropriate. We’ve since adopted the term as one word, malapropos (as we have its opposite, apropos).
Metaphor is the use of words or phrases to suggest something else, for a more vivid effect. Here’s an example: The moon was a ghostly galleon. The moon was not actually a ghostly galleon, of course, but that phrase conjures a poetic image much better than “the moon appeared to be large and was somewhat obscured by clouds.”
There’s lots of good fun to be had from mixing metaphors but I find myself thinking about Yogi Berra and some of his deathless quotations, like “when you come to a fork in the road, take it.” I can’t think that we should exclude Berra from the ranks of malaphor creators, just because he managed to get as much fun out of a single metaphor as most people can with two. In fact, many of his remarks weren’t even based on a metaphor, so they wouldn’t qualify as malaphors anyway. Maybe we need a different word to refer to them.
The Malaphor King collects prime examples of malaphors.