Synonyms of the word

impenetrable

• adj. Not penetrable.
• adj. (figuratively) Incomprehensible; inscrutable.

dense

• adj. Having relatively high density.
• adj. Compact; crowded together.
• adj. Thick; difficult to penetrate.
• adj. Opaque; allowing little light to pass through.
• adj. Obscure, or difficult to understand.
• adj. (mathematics, topology) Being a subset of a topological space that approximates the space well. See Wikipedia…
• adj. (of a person) Slow to comprehend; of low intelligence.

heavy

• adj. (of a physical object) Having great weight.
• adj. (of a topic) Serious, somber.
• adj. Not easy to bear; burdensome; oppressive.
• adj. (Britain, slang, dated) Good.
• adj. (dated, late 1960s, 1970s, US) Profound.
• adj. (of a rate of flow) High, great.
• adj. (slang) Armed.
• adj. (music) Louder, more distorted.
• adj. (of weather) Hot and humid.
• adj. (of a person) Doing the specified activity more intensely than most other people.
• adj. (of food) High in fat or protein; difficult to digest.
• adj. Of great force, power, or intensity; deep or intense.
• adj. Laden to a great extent.
• adj. Laden with that which is weighty; encumbered; burdened; bowed down, either with an actual burden, or with…
• adj. Slow; sluggish; inactive; or lifeless, dull, inanimate, stupid.
• adj. Impeding motion; cloggy; clayey.
• adj. Not raised or leavened.
• adj. Having much body or strength; said of wines or spirits.
• adj. (obsolete) With child; pregnant.
• adv. heavily.
• adv. (India, colloquial) very.
• n. A villain or bad guy; the one responsible for evil or aggressive acts.
• n. (slang) A doorman, bouncer or bodyguard.
• n. (aviation) A large multi-engined aircraft.
• v. (often with "up") To make heavier.
• v. To sadden.
• v. (Australia, New Zealand, informal) To use power and/or wealth to exert influence on, e.g., governments…
• adj. Having the heaves.

incomprehensible

• adj. Impossible or very difficult to understand.

thick

• adj. Relatively great in extent from one surface to the opposite in its smallest solid dimension.
• adj. Measuring a certain number of units in this dimension.
• adj. Heavy in build; thickset.
• adj. Densely crowded or packed.
• adj. Having a viscous consistency.
• adj. Abounding in number.
• adj. Impenetrable to sight.
• adj. Difficult to understand, or poorly articulated.
• adj. (informal) Stupid.
• adj. (informal) Friendly or intimate.
• adj. Deep, intense, or profound.
• adj. (Britain, dated) troublesome; unreasonable.
• adj. (slang, chiefly of women) Curvy and voluptuous, and especially having large hips.
• adv. In a thick manner.
• adv. Thickly.
• adv. Frequently; in great numbers.
• n. The thickest, or most active or intense, part of something.
• n. A thicket.
• n. (slang) A stupid person; a fool.
• v. (archaic, transitive) To thicken.

uncomprehensible

• adj. Incomprehensible.