heffalump

The story

Probably a childish mispronunciation of elephant, perhaps influenced by half a lump (as in "I'll have half a lump of sugar in my tea"), coined by the English author Alan Alexander Milne (1882–1956) as the name of an imaginary animal in his book Winnie-the-Pooh (1926). The animal was not described in the book, but the illustrator Ernest Howard Shepard (1879–1976) depicted it as an elephant. Sense 2 (“something which is elusive”) refers to the fact that in Milne’s book the characters Winnie-the-Pooh and Piglet set a trap for, but are unable to capture, a heffalump.