Both the onset and the coda can consist of more than one consonant, also known as a consonant cluster. The combination /st/ is a consonant cluster (CC) used as onset in the word stop, and as coda in the word post. There are many CC onset combinations permitted in English phonotactics, as in black, bread, trick, twin, flat and throw. Note that liquids (/l/, /r/) and a glide (/w/) are being used in second position.

English can actually have larger onset clusters, as in the words stress and splat, consisting of three initial consonants (CCC). The phonotactics of these larger onset consonant clusters is not too difficult to describe. The first consonant must always be /s/, followed by one of the voiceless stops (/p/, /t/, /k/) and a liquid or glide (/l/, /r/, /w/). You can check if this description is adequate for the combinations in splash, spring, strong, scream and square. Does the description also cover the second syllable in the pronunciation of exclaim? How about /ɛk-skleɪm/? Remember that it is the onset of the syllable that is being described, not the beginning of the word.

It is quite unusual for languages to have consonant clusters of this type. Indeed, the syllable structure of many languages (e.g. Japanese) is predominantly CV. It is also noticeable in English that large consonant clusters may be reduced in casual conversational speech, particularly if they occur in the middle of a word. This is just one example of a process that is usually discussed in terms of coarticulation effects.