cluster (n.)

A term used in the analysis of CONNECTED SPEECH to refer to any sequence of adjacent CONSONANTS, especially those occurring INITIALLY or FINALLY in a SYLLABLE, such as the initial [br-] of bread, or the final [-st] of best. Not all possible combinations of consonants occur in a LANGUAGE. Initially in syllables in English, for example, clusters are not possible with  or [z]. Up to three consonants can occur initially, as in [spr-], [spl-], [skw-]; up to four can occur finally, as in glimpsed [-mpst] and twelfths [-lfθs].