(1):

(v. t.) To strengthen; to confirm.

(2):

(v. t.) To make more frequent; as, to thicken blows.

(3):

(v. t.) To make thick (in any sense of the word).

(4):

(v. t.) To render dense; to inspissate; as, to thicken paint.

(5):

(v. t.) To make close; to fill up interstices in; as, to thicken cloth; to thicken ranks of trees or men.

(6):

(v. i.) To become thick.