What is "to block out"

Block \Block\ (bl[o^]k), v. t. [imp. & p. p. Blocked (bl[o^]kt); p. pr. & vb. n. Blocking.] [Cf. F. bloquer, fr. bloc block. See Block, n.]

1. To obstruct so as to prevent passage or progress; to prevent passage from, through, or into, by obstructing the way; -- used both of persons and things; -- often followed by up; as, to block up a road or harbor; to block an entrance.

   With moles . . . would block the port.
   --Rowe.

   A city . . . besieged and blocked about.
   --Milton.

2. To secure or support by means of blocks; to secure, as two boards at their angles of intersection, by pieces of wood glued to each.

3. To shape on, or stamp with, a block; as, to block a hat.

4. to cause (any activity) to halt by creating an obstruction; as, to block a nerve impulse; to block a biochemical reaction with a drug.

   To block out, to begin to reduce to shape; to mark out roughly; to lay out; to outline; as, to block out a plan.