Definitions of thickly:

• adverb:   spoken with poor articulation as if with a thick tongue

  Example: "After a few drinks he was beginning to speak thickly"

• adverb:   with thickness; in a thick manner

  Example: "Spread 1/4 lb softened margarine or cooking fat fairly thickly all over the surface"

• adverb:   with a thick consistency
• adverb:   in a concentrated manner

  Example: "A thickly populated area"

• adverb:   in quick succession