Rarefied

Adjective

 * 1) Esoteric.
 * 2)  Less dense than usual.
 * The air at the top of a high mountain is rarefied.

Thesaurus
adulterated, air-built, airy, attenuate, attenuated, boyish, chimerical, clannish, cliquish, cloud-built, cut, dainty, delicate, diaphanous, dilute, diluted, dreamlike, elevated, esoteric, ethereal, exalted, exclusive, fanciful, fatuitous, fatuous, fine, fine-drawn, finespun, flimsy, frail, gaseous, gauzy, girlish, gossamer, gossamery, gracile, high, illusory, imaginary, insubstantial, lacy, lean, light, lofty, misty, noble, papery, phantomlike, private, rare, reduced, scant, scanty, select, shadowy, slender, slenderish, slight, slight-made, slim, slimmish, slinky, small, sparse, spirituous, sublime, subtile, subtle, svelte, sylphlike, tenuous, thin, thin-bodied, thin-set, thin-spun, thinned, thinned-out, thinnish, threadlike, uncompact, uncompressed, unreal, unsubstantial, vague, vaporous, wasp-waisted, watered, watered-down, watery, weak, willowy, windy, wiredrawn, wispy

Alternative forms

 * rarified