Origins
The word 'syllable' entered English in the late fourteenth century from Old French 'sillabe,' from Latin 'syllaba,' from Greek 'syllabḗ' (συλλαβή). The Greek word means literally 'a taking together' or 'a grasping together,' from the prefix 'syn-' (σύν, together) and the verb 'lambánein' (λαμβάνειν, to take, to seize, to grasp). A syllable is, in its original metaphor, a handful of sounds — letters grabbed together to form a single unit of speech.
The Greek verb 'lambánein' has a complex morphology, with the aorist (past) stem 'lab-' and a reduplicated form 'lēlab-.' The PIE root behind it is debated, with some scholars connecting it to *sleh₂gʷ- (to seize). Through various Greek formations, this root gave English 'epilepsy' (a seizing upon), 'catalepsy' (a seizing down), 'syllable,' and 'syllabus.'
The connection between 'syllable' and 'syllabus' is one of the most entertaining accidents in etymological history. The word 'syllabus' does not actually exist in Classical Latin or Greek. It originated as a misreading in a fifteenth-century manuscript of Cicero's 'Ad Atticum,' where the Greek accusative plural 'sittybas' (σιττύβας, parchment labels for scrolls) was incorrectly transcribed as 'syllabos' or 'syllabus.' The error was propagated, and 'syllabus' came to be understood as 'a list, a summary' — influenced by the existing word 'syllable' and its connotation of 'things taken together.' The word became firmly established in English by the seventeenth century, and when the Vatican issued its 'Syllabus Errorum' (Syllabus of Errors) in 1864, the ghost word achieved permanent respectability.
Spelling and Pronunciation
In phonology, a syllable is the fundamental unit of prosodic organization. Every syllable has a nucleus (typically a vowel), optionally preceded by an onset (one or more consonants) and followed by a coda (one or more consonants). The word 'strengths' is a single syllable with a complex structure — three consonants in the onset, one vowel, and four consonants in the coda — one of the most complex syllable structures permitted in English.
Languages differ dramatically in the syllable structures they allow. Hawaiian permits only open syllables (consonant + vowel), giving it its characteristic flowing sound. Japanese is similar, with most syllables being CV or just V. English and German, by contrast, permit complex consonant clusters, allowing words like 'strengths' and 'Herbst' (autumn). Some Caucasian and Salishan languages permit syllables with no vowel at all, consisting entirely of consonants.
The related terms 'monosyllabic' (one syllable), 'disyllabic' (two syllables), 'trisyllabic' (three), and 'polysyllabic' (many) use Greek number prefixes. 'Monosyllabic' has also developed the figurative sense of 'using few words, taciturn,' since a person giving one-syllable answers ('yes,' 'no,' 'fine') seems uncommunicative.