From The Collaborative International Dictionary of English v.0.48 :
Thickly \Thick"ly\, adv.
In a thick manner; deeply; closely.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
thickly
adv 1: spoken with poor articulation as if with a thick tongue;
"after a few drinks he was beginning to speak thickly"
2: in a concentrated manner; "old houses are often so densely
packed that perhaps three or four have to be demolished for
every new one built"; "a thickly populated area" [syn:
densely, thickly] [ant: thinly]
3: with a thick consistency; "the blood was flowing thick" [syn:
thickly, thick] [ant: thin, thinly]
4: with thickness; in a thick manner; "spread 1/4 lb softened
margarine or cooking fat fairly thickly all over the
surface"; "we were visiting a small, thickly walled and
lovely town with straggling outskirt" [ant: lightly,
thinly]
5: in quick succession; "misfortunes come fast and thick" [syn:
thick, thickly]