/θrʌʃ/
[noun] A medium-sized songbird known for its beautiful, melodious singing and spotted breast, found across Europe and North America. The word also refers to a common fungal infection that causes white patches in the mouth or other moist areas of the body.
'Thrush' the bird and 'thrush' the infection are almost certainly two completely different words that just happen to sound identical.
The thrush that sings from garden hedges and woodland branches is one of the oldest bird names in the English language. It descends directly from the Old English word 'þrysce', which was already in use more than a thousand years ago to describe exactly this family of spotted, sweet-voiced birds. That Old English form connects back to Proto-Germanic 'þruskjō', and further still to Proto-Indo-European roots related to the idea of the thrush — a bird that clearly made enough of an impression on early human communities that they named it consistently across many languages and centuries.
The Germanic connection runs remarkably deep. Old High German had 'drosca' and 'droscala', which evolved into Middle High German 'droschel', and eventually into modern German 'Drossel', still used today for thrushes. Old Norse had 'þröstr'. These are all cousins, branching from the same Proto-Germanic ancestor, preserving across a dozen modern languages the memory of a bird that ancient northern European peoples clearly loved and noticed. In Old English itself, a related form 'þrostle' also existed alongside 'þrysce', and 'throstle' survived in English poetry and dialect well into the 19th century as a poetic name for the song thrush specifically.
When Middle English reshaped the sounds of Old English, 'þrysce' gradually shifted toward 'thrush', losing the '-ce' ending and settling into the clean, single-syllable form we use today. By the 14th century, the word appears in Middle English texts in recognisably modern form. The song thrush, the mistle thrush, the fieldfare — all fell under this comfortable umbrella name, a word sturdy enough to hold a whole family of birds.
The second meaning of 'thrush' — the fungal infection caused by Candida yeast — is almost certainly a completely separate word that arrived in English by a different route. Its earliest recorded uses in English date to the 17th century, and its precise origin is disputed. Some scholars suggest a Scandinavian connection, pointing to Danish and Norwegian 'trøske' for the same condition. Others have proposed links to older words meaning 'to dry out' or referring to cracking and soreness. What seems clear is that this 'thrush' did not grow from the same Old English root as the bird — the resemblance is a coincidence of sound, one of those delightful accidents that makes English so endlessly interesting.
The bird's name, meanwhile, has inspired poets for centuries precisely because the thrush is such a noticeable, unforgettable singer. Thomas Hardy wrote of the 'darkling thrush' in one of his most famous poems, and the bird appears throughout English literature as a symbol of joy, perseverance, and the consolations of nature. That such an ancient word — older than the Norman Conquest, older than Middle English itself — should still sit so naturally on the tongue today is its own quiet kind of miracle. The thrush sings on, and its name endures just as faithfully.