From The Collaborative International Dictionary of English v.0.48 :
Thinly \Thin"ly\, a.
In a thin manner; in a loose, scattered manner; scantily; not
thickly; as, ground thinly planted with trees; a country
thinly inhabited.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
thinly
adv 1: without force or sincere effort; "smiled thinly"
2: without viscosity; "the blood was flowing thin" [syn:
thinly, thin] [ant: thick, thickly]
3: in a small quantity or extent; "spread the margarine thinly
over the meat"; "apply paint lightly" [syn: thinly,
lightly] [ant: thickly]
4: in a widely distributed manner; "thinly overgrown
mountainside" [ant: densely, thickly]