【Close】 , 【dense】 , 【compact】 , 【thick】 are comparable when they mean having constituent parts (as filaments, particles, cells, or atoms) that are massed tightly together.

【Close】 may apply to the texture or weave of something. More often, however, the term applies to something that is made up of a number of single things pressed or seemingly pressed together. Especially as applied to literary expression,  【close】 implies a compression of what is to be said into the fewest and most telling words possible.

【Dense】 applies to something in which the arrangement of parts or units is exceedingly 【close】 . The term commonly implies impenetrability and in extended use may lose the basic notion of 【close】 packing of parts.

【Compact】 suggests 【close】 and firm union or consolidation of parts, especially within a small compass; it often also implies neat or effective arrangement.

【Thick】  (see also STOCKY) usually applies to something which is condensed or is made up of abundant and concentrated parts.