What does "trepan" mean?

Additional senses

1. 2.To perforate (the skull) with a trepan, so as to remove a portion of the bone, and thus relieve the brain from pressure or irritation; to perform an operation with the trepan.
2. 3.A snare; a trapan. Snares and trepans that common life lays in its way. South.
3. 4.a deceiver; a cheat. He had been from the beginning a spy and a trepan. Macaulay.
4. 5.To insnare; to trap; to trapan. Guards even of a dozen men were silently trepanned from their stations. De Quincey.