Definition of

Thickly

1. (adv, all) in a concentrated manner
   a thickly populated area
2. (adv, all) in quick succession
3. (adv, all) spoken with poor articulation as if with a thick tongue
4. (adv, all) with thickness; in a thick manner
   we were visiting a small, thickly walled and lovely town with straggling outskirt
5. (adv, all) with a thick consistency

via WordNet, Princeton University