mysterious

As adjectives the difference between serious and mysterious

is that serious is without humor or expression of happiness; grave in manner or disposition; earnest; thoughtful; solemn while mysterious is of unknown origin.

As adjectives the difference between mysterious and unprecedented

is that mysterious is of unknown origin while unprecedented is never before seen or done, without precedent.

As adjectives the difference between indistinct and mysterious

is that indistinct is (of an image etc) not clearly defined or not having a sharp outline; faint or dim while mysterious is of unknown origin.

As adjectives the difference between mysterious and profound

is that mysterious is of unknown origin while profound is descending far below the surface; opening or reaching to great depth; deep.

As a noun profound is

(obsolete) the deep; the sea; the ocean.

As a verb profound is

(obsolete) to cause to sink deeply; to cause to dive or penetrate far down.

As an adjective mysterious

is of unknown origin.

As a verb great is

.

As adjectives the difference between mysterious and reticent

is that mysterious is of unknown origin while reticent is reluctant; reticent.