In 1593 Gabriel Harvey wrote a piece called Pierce’s Supererogation, or a New Praise of the Old Ass. It was basically an extended insult of a fellow named Thomas Nashe, and in part he refers to him as “…a dodkin author, whose two swords are like the horns of a hodmandod…”. In this he was evoking the subject of an ancient English riddle:
“Though not a cow I have horns;
Though not an ass I carry a pack-saddle;
And wherever I go I leave silver behind me.”
Likewise, in 1654 John Webster wrote Applus and Virginia in which he said “I am an Ant, a Gnat, a worm..a Hodmondod amongst flies.” Other contemporary writers also used “hoddy-doddy” and “hodman-did” to mean the same thing.
Etymology is no help here; nobody knows where “hodmandod” came from. It might be related to “dod”, but that’s just as obsolete as the first word, and its origin is also a complete mystery. It was probably a word from a local dialect that became more widely used a few centuries ago. And it’s not completely obsolete. Although it hasn’t been in widespread use since the 1800s, reportedly it can still be heard in at least a dialect around Norfolk, England.
There’s a similar-sounding word that used to be confused with hodmandod: “dudman.” But they’re not at all related; a “dudman” was a scarecrow — “duds” is fading out, but is still an obscure term for clothing. Because you’d only use your old, ragged clothing for a scarecrow, “duds” came to mean tattered, useless clothes, and that’s where the figurative sense of “dud” came from: something that’s of no use or does not work.
But back to hodmandod. If you haven’t guessed at this point — and the riddle is really the only decent clue here; there’s nothing in the sound or derivation of “hodmandod” to suggest its meaning — a “hodmandod” is a snail.