Svelte

From French svelte, from Italian svelto ("stretched out"), from Vulgar Latin exvellere: ex + vellere ("to pluck, stretch").

Full definition of svelte

1990, Eve Kosofsky Sedgwick, Epistemology of the Closet, 2008, page 24,Psychoanalytic theory...seemed to promise to introduce a certain becoming amplitude into discussions of what different people are like â€” only to turn, in its streamlined trajectory across so many institutional boundaries, into the sveltest of metatheoretical disciplines, sleeked down to such elegant operational entities as the mother, the father, the preoedipal, the oedipal, the other or Other.
2007, January 19, Charles Isherwood, Welterweight Bialystock Treads Softly on Big Shtick, Clearly the producers of â€œThe Producersâ€ were so little inclined to tinker with a winning formula that they chose not to excise a few lines of dialogue to accommodate the svelter physique of their new leading man, preposterous though it is that anyone in a fit of pique would deride a fellow as â€œonce-husky.â€
2009, Kim Bloomer, Animals Taught Me That, page 73,My first priority was to help Trumps lose her pudgy look and gain a healthier, svelter size.
2010, M. S. Simpson, Kabuki in a G-String, page 158,If her dream of being naked in front of Simon were to come true â€“ and she knew, somehow, that it would â€“ she needed to be the sveltest version of herself that had ever existed. Fries wouldn't help peel away those pounds.

1942, Beryl Markham, West with the Night:Peering down from the cockpit at grazing elephant, you have the feeling that what you are beholding is wonderful, but not authentic. It is not only incongruous in the sense that animals simply are not as big as trees, but also in the sense that the twentieth century, tidy and svelte with stainless steel as it is, would not possibly permit such prehistoric monsters to wander in its garden.

Used mainly as a compliment, whereas words like thin, scrawny and skinny could be used in negative connotations.