Origins
The word 'song' is among the most ancient in the English language, descending through an unbroken Germanic lineage from Proto-Indo-European. It comes from Old English 'sang' or 'song' (both forms existed), from Proto-Germanic *sangwaz, derived from the PIE root *sengʷʰ-, meaning 'to sing' or 'to chant.' The word is the nominal derivative of the verb 'sing' — a song is, at its most basic, 'that which is sung.'
The PIE root *sengʷʰ- is notable for its possible connection to incantation and ritual speech. In several ancient Indo-European traditions, singing and magical chanting were not clearly distinguished. The Greek cognate — if the connection holds — may relate to 'omphḗ' (divine voice, oracle), though this derivation is contested. What is more secure is the purely Germanic lineage: Old Norse 'söngr,' Gothic 'saggws,' Old High German 'sang,' Dutch 'zang,' and Swedish 'sång' all descend from the same Proto-Germanic form.
In Old English, 'sang' had a broader semantic range than modern 'song.' It encompassed not only vocal musical composition but also poetry more generally — the Beowulf poet uses 'sang' to describe heroic verse that might or might not have been performed musically. This conflation of poetry and song reflects the oral culture of early Germanic society, in which most poetry was performed aloud, often to musical accompaniment. The modern English distinction between 'song' (musical) and 'poem' (literary) would have been largely meaningless to an Anglo-Saxon audience.
Middle English
The word underwent surprisingly little change through the Middle English period. Both 'song' and 'sang' continued in use, with 'song' gradually becoming the dominant form. The vowel did not participate in the Great Vowel Shift, as it was a short vowel before a nasal consonant cluster, a position that resisted the shift's transformations.
English has generated a rich vocabulary of compounds from 'song.' 'Songbird' dates to the seventeenth century. 'Songster' (a singer) is much older, attested from Old English. 'Swan song,' meaning a final performance before death or retirement, translates German 'Schwanengesang,' which itself translates a Greek belief recorded by Plato and Aristotle — that the mute swan, silent all its life, sings one achingly beautiful song just before dying. The belief is zoologically false, but the metaphor proved so compelling that it has persisted for over 2,400 years and naturalized into languages across Europe.
The phrase 'for a song' (meaning very cheaply) dates to the late sixteenth century and appears in Shakespeare. The logic behind it is that songs, being immaterial, were considered nearly worthless in a commercial sense — a street musician's performance could be had for a penny or nothing at all.
Proto-Indo-European Roots
The relationship between 'song' and 'sing' illustrates a common Germanic word-formation pattern: the verb root undergoes ablaut (vowel alternation) to form the noun. 'Sing' has the vowel /ɪ/, while 'song' has /ɒ/ — the same ablaut pattern visible in pairs like 'drink/drunk' and 'ring/rung.' This vowel alternation is inherited directly from Proto-Indo-European, where ablaut was the primary mechanism for deriving nouns from verbs.
Today 'song' remains one of the most frequently used words in English, appearing in contexts from the sacred ('Song of Songs') to the commercial ('hit song') to the scientific (the 'song' of whales and birds, extended by analogy from human vocal music to animal vocalizations that share structural features like phrasing, repetition, and melodic contour).