impenetrable

Populous is a related term of impenetrable.

As adjectives the difference between populous and impenetrable

is that populous is having a large population while impenetrable is impenetrable.

Close is a related term of impenetrable.

As adjectives the difference between close and impenetrable

is that close is closed, shut while impenetrable is impenetrable.

As a verb close

is (label) to remove a gap.

As a noun close

is an end or conclusion or close can be an enclosed field.

Impenetrable is a synonym of solid.

As an adjective impenetrable

is impenetrable.

As an acronym solid is

(programming|object-oriented).

Enigmatic is a related term of impenetrable.

As adjectives the difference between enigmatic and impenetrable

is that enigmatic is enigmatic while impenetrable is impenetrable.

Mysterious is a synonym of impenetrable.

As adjectives the difference between mysterious and impenetrable

is that mysterious is of unknown origin while impenetrable is impenetrable.

Narrow is a related term of impenetrable.

As adjectives the difference between narrow and impenetrable

is that narrow is having a small width; not wide; slim; slender; having opposite edges or sides that are close, especially by comparison to length or depth while impenetrable is impenetrable.

As a verb narrow

is to reduce in width or extent; to contract.

As a noun narrow

is (chiefly|in the plural) a narrow passage, especially a contracted part of a stream, lake, or sea; a strait connecting two bodies of water.

As adjectives the difference between restricted and impenetrable

is that restricted is limited within bounds while impenetrable is not penetrable.

As a verb restricted

is past tense of restrict.

As adjectives the difference between impenetrable and thick

is that impenetrable is not penetrable while thick is relatively great in extent from one surface to the opposite in its smallest solid dimension.

As an adverb thick is

in a thick manner.

As a noun thick is

the thickest, or most active or intense, part of something.

As a verb thick is

to thicken.

Impenetrable is a related term of intense.

As adjectives the difference between impenetrable and intense

is that impenetrable is impenetrable while intense is strained; tightly drawn.

Impenetrable is a related term of unknown.

As adjectives the difference between impenetrable and unknown

is that impenetrable is impenetrable while unknown is not known; unidentified; not well known.

As a noun unknown is

(algebra) a variable (usually x'', ''y'' or ''z ) whose value is to be found.