WordNet sense 1 (the location of something surrounded by other things):

midst

WordNet sense 2 (having a relatively high resistance to flow):

viscous

WordNet sense 3 (permitting little if any light to pass through because of denseness of matter):

dense, heavy, impenetrable

WordNet sense 4 (transformed from a liquid into a soft semisolid or solid mass):

grumose, grumous

WordNet sense 5 (thickened or coalesced in soft thick lumps (such as clogs or clots)):

clotted

WordNet sense 6 (having a relatively large diameter):

fat

WordNet sense 7 (relatively thick from top to bottom):

deep

WordNet sense 8 (in an extreme degree):

intense

WordNet sense 9 (spoken as if with a thick tongue):

slurred

WordNet sense 10 (poorly articulated or enunciated, or drowned by noise):

unintelligible

WordNet sense 11 (heavy and compact in form or stature):

compact, heavyset, stocky, thickset, compact

WordNet sense 12 (gathered together or made less diffuse):

concentrated

WordNet sense 13 (with a thick consistency):

thickly

WordNet sense 14 ((used informally) associated on close terms):

chummy, buddy-buddy

WordNet sense 15 (close in relevance or relationship):

close

WordNet sense 16 (used informally):

boneheaded, fatheaded, thickheaded, blockheaded, loggerheaded, thick-skulled, wooden-headed

WordNet sense 17 (lacking or marked by lack of intellectual acuity):

stupid

WordNet sense 18 (present in great quantity):

abundant