Oh, to be svelte. To be as light as felt, a suave fellow or a lass as light as a velleity, not swelling like Elvis but sweltering hot: no thicker than the drop of sweat that falls down your brow at the sight or the plucked eyebrows of a stylish lady. And stylish, yes, svelte always seems stylish, fitted, bespoke tailored.
For this is a word thick with connotation. Look at its map on the Visual Thesaurus: svelte connects to three nodes, one of which branches to slight, slim, slender, another to lithe, lissome, lissom, supple, sylphlike (I have to catch my breath after the frisson that runs down me saying that word), lithesome, and again slender, and the third to polished, refined, and urbane. The svelte person may be lean but is not meagre; this is a person of substance as Cognac is a beverage of substance. To be svelte is to have the air of an eau-de-vie of humanity: a special one plucked out from among the many. I was in my youth slender by nature but could barely manage svelte at even the best of times.
Obviously the word seems to privilege leanness, although I would not say it necessarily implies that a person who is not lean cannot be attractive or of substance — there are other words for them; this just isn't a word for those with much more than a whippet's physique.
Look at the word: you can read into its forms the traits of its object if you wish, the lithe s, the plunging v-neck on the evening gown or the lapels of a tuxedo, the svelte tall man l and his svelte consort t, and the eyes e e that watch them pass. Say it: your lips barely move but your lower lip just lightly brushes against your teeth, making the small gesture that might pass over the soft, light lips of a lean beauty as she thinks carefully whether she can keep herself from kissing this dashing fellow, or over the fellow's lips as he, too, uncertainly prepares for possible osculation with this sylphlike (ahhh) lass.
You can also guess that the word may have roots in Italian and French. The silent e ending that doesn't make the previous vowel "long" is a sign of French, but the sv onset is not — much more likely Italian, since the word doesn't overall look Sanskrit or Swedish. And in fact English got this word unchanged from French, which modified it from Italian svelto, past participle of svellere 'pull out,' originating with Latin ex 'out' plus vellere 'pull, pluck.'
There aren't too many other words that have made it into English with sv at the start; the OED lists 12, of which half are proper nouns, and four are from Sanskrit, four Scandinavian, only one Italian. The fictitious character Svengali is one of the remainder: the mesmeric impresario of the chanteuse Trilby. The least svelte term of the bunch is the linguistic term svarabhakti, which is borrowed from Sanskrit. It names the insertion of an excrescent vowel sound into a word, as when one says "fillum" for film — or "sa-velt" for svelte: an unfashionable thickness.