In linguistics, a consonant cluster (CC) is a group of two or more consonant sounds that come before (called an onset), after (called a coda) or between (called medial) vowels. Also known simply as a cluster, these occur naturally in written and spoken English - though sometimes may be altered phonetically.
This process, called consonant cluster simplification (or reduction) sometimes occurs when at least one consonant in a sequence of adjacent consonants is elided or dropped. In everyday speech, for instance, the phrase "best boy" may be pronounced "bes' boy," and "first time" may be pronounced "firs' time."
Onset consonant clusters may occur in two or three initial consonants, wherein three are referred to as CCC while coda consonant clusters can occur in two to four consonant groups.
Common Consonant Clusters
The written English language contains up to 46 permissible two-item initial consonant clusters, ranging from the common "st" to the less common "sq," but only 9 permissible three-item consonant clusters, as Michael Pearce posits in his book The Routledge Dictionary of English Language Studies.
Pearce illustrates the common three-item initial consonant clusters in the following words: "spl/ split, /spr/ sprig, /spj/ spume, /str/ strip, /stj/ stew, /skl/ sclerotic, /skr/ screen, /skw/ squad, /skj/ skua," wherein every word must start with an "s," be followed by a voiceless stop like "p" or "t" and a liquid or glide like "l" or "w."
In terms of codas, or consonant clusters that end words, they may contain up to four items, though they are often truncated in connected speech if the consonant cluster is too long, as in the word "glimpsed" being acceptably written as "glimst."
Consonant Cluster Reduction
In spoken English and rhetoric, oftentimes consonant clusters will be truncated naturally to increase speed or eloquence of speech, oftentimes dropping the same consonant if it occurs at the end of one word and again at the beginning of the next. This process, called consonant cluster reduction, is relatively variable but confined by linguistic factors that inhibit the operation of reducing these words.
Walt Wolfram, writing in Dialect in Society, expounds, "with respect to the phonological environment that follows the cluster, the likelihood of reduction is increased when the cluster is followed by a word beginning with a consonant."
What this means for average English users is that cluster reduction is more common in phrases like "west coast or cold cuts" than in "west end or cold apple."
This technique can also be found in poetry to force similar-sounding words with different consonant endings to rhyme. Take for example the words test and desk, which don't rhyme in their original form, but if one uses consonant cluster reduction, the rhyme "Sittin' in my des', takin' my tes'" can be forced through truncation, as Lisa Green describes in African American English: A Linguistic Introduction, this is most common in the poetic raps of African American origins in the United States.