\Thick"en\, v. t. [imp. & p. p. {Thickened}; p. pr. &
vb. n. {Thickening}.]
To make thick (in any sense of the word). Specifically:
(a) To render dense; to inspissate; as, to thicken paint.
(b) To make close; to fill up interstices in; as, to thicken
    cloth; to thicken ranks of trees or men.
(c) To strengthen; to confirm. [Obs.]
          And this may to thicken other proofs. --Shak.
(d) To make more frequent; as, to thicken blows.

\Thick"en\, v. i.
To become thick. ``Thy luster thickens when he shines by.''
--Shak.
      The press of people thickens to the court. --Dryden.
      The combat thickens, like the storm that flies.
                                               --Dryden.