Svelte \svelt\ or \sfelt\ , adjective;
1. Slender, especially gracefully slender in figure; lithe
2. Suave; blandly urbane
Dating to around 1817, the origin of svelte is French svelte ("slim, slender") from Italian svelto ("slim, slender"). The Italian word originally meant "pulled out, lengthened" from the past participle of svellere ("to pluck or root out"), which derives from Vulgar Latin *exvellere based on the Latin compound ex- + vellere ("out" + "to pluck, stretch").
One of the words in the definition comes from Old English: lithe.
The Old English spelling was liðe and it meant "soft, mild, gentle, meek." It derives from Proto-Germanic *linthijaz from the Proto-Indo-European base *lent- ("flexible"). In Middle English lithe was used to talk about the weather, and the current meaning of "easily flexible" dates to the 1400's.