Of little thickness
flimsy, slim, slight, tenuous, attenuated, diaphanous, sheer, rare, sleazy, permeable, paper-thin, wafer-sliced; see also transparent 1.
Antonyms thick*, heavy, coarse.
Slender
slim, lean, skinny, scraggy, lank, lanky, spindly, spare, gaunt, bony, wan, rangy, skeletal, scrawny, lanky, delicate, wasted, haggard, emaciated, rawboned, shriveled, wizened, rickety, spindling, pinched, starved; see also dainty 1.
Antonyms fat*, obese, heavy.
Sparse
scarce, insufficient, deficient; see inadequate 1.
Having little content
sketchy, slight, insubstantial, weak-kneed, vapid, weak, light, feeble, flat, diluted, thinly stretched; see also shallow 1, 2.
Antonyms thick*, solid, substantial.
Having little volume
faint, shrill, piping, weak, rarefied, tenuous, attenuated, fragile, small, tiny, featherweight, bodiless, disembodied, ethereal, shaky; see also light 7.
Antonyms thick*, heavy, dense.