1. Any of various invertebrates, as those of the phyla Annelida, Nematoda, Nemertea, or Platyhelminthes, having a long, flexible, rounded or flattened body, often without obvious appendages.
2. Any of various crawling insect larvae, such as a grub or a caterpillar, having a soft elongated body.
3. Any of various unrelated animals, such as the shipworm or the slowworm, resembling a worm in habit or appearance.
4.  
   1. Something, such as the thread of a screw or the spiral condenser in a still, that resembles a worm in form or appearance.
   2. The spirally threaded shaft of a worm gear.
5. An insidiously tormenting or devouring force: “felt the black worm of treachery growing in his heart” (Mario Puzo).
6. A person regarded as pitiable or contemptible.
7. worms Pathology. Infestation of the intestines or other parts of the body with worms or wormlike parasites; helminthiasis.
8. Computer Science. A malicious program that replicates itself until it fills all of the storage space on a drive or network.