(n.) the omission of a repeated or similar-sounding syllable in the pronunciation of a word
When two identical or similar-sounding letters or syllables fall side by side one another in a word, it’s often the case that one of them is omitted when the word is pronounced. This is haplology—a form of omission reduces probably to “probly”, practically to “practly”, February to “Febry”, and library to “libry”.
Many of these haplological contractions are considered non-standard, and are typically best avoided in more careful or formal speech; as a result, they’re often speciously considered annoyances and bugbears by many people, alongside the likes of expresso coffees and the Specfic Ocean.
But haplologies aren’t always considered errors per se, as some of them have become the standard form of certain words in our language.
English adverbs, for instance, are formed by adding the suffix –ly to a root adjective; it’s this that gives us words like hardly, strongly, slowly and quickly. But when the root adjective already ends in a Y, we have a sub-rule in English that changes this Y to an I—giving us the likes of happily, angrily, cosily and friendlily. When the adjective already ends in an L sound, however, we have another rule that relies on haplology to cast one of these duplicate Ls out. So able becomes ably, not *ablely. Gentle becomes gently, not *gentlely. Noble becomes nobly, not noblely. Ample becomes amply, and so on. (This being English, of course, there are still some exceptions: agile and stale become agilely and stalely, not *agily and *staley.)
Haplology not only affects the morphology of some of our words, but it creeps into their etymologies too. Where does an armourer work? In an armoury, not an *armourery. The belief in or worship of demons is called demonomy, not *demononomy. The study of the devil is called diabology, not *diabolology. And onomancy is a form of divination based on reading the letters of someone’s name; had haplology not come into play when that word was in its etymological infancy, then it would be called *onomatomancy.
Oddly, this process didn’t affect the etymological creation of the word haplology itself. When it was coined in the late 1800s (derived from a Greek root essentially meaning ‘single’ or ‘simple’) its somewhat clumsy neighbouring L sounds remained unreduced. So this is all rather counterintuitively called haplology, not *haplogy.