-cule Also -cle, -icle, and -culus.
[French -cule, derived from Latin -culus, -cula or -culum.]
The original sense of the Latin endings was as a diminutive, though this has largely been lost in English. Words in -cule include graticule (Latin cratis, a hurdle), a series of fine lines used as a measuring scale; molecule (Latin moles, mass), a group of atoms bonded together. Words in -cle (of which -icle is a variant in which the i is contributed by the Latin stem) include article, particle, carbuncle, cubicle, manacle, and testicle.
Some words exist in more than one form, with those in -(i)cle being more general than those in -cule or -culus (the latter perpetuating the masculine form of the Latin ending), which are commoner in scholarly contexts. An example is fascicle (from Latin fascis, a bundle) for an instalment of a printed book, which sometimes appears as fascicule; in anatomy and biology the word is more commonly fasciculus for a bundle of structures, such as nerve fibres or conducting vessels.
Words that primarily exist in the -ulus ending include homunculus (Latin homo, man), a very small human figure; the genus of the bindweed, convolvulus (literally a little thing bound together); and apiculus, a minute point or tip.