Past tense and past participle of countersink.(verb)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "countersunk" in a sentence
"A surgeon drilled an inch and a half into my skull, countersunk a ceramic-encased microchip behind my left ear, and threaded sixteen electrodes into my inner ear."
"The computational elements could be countersunk into the skull under the skin, as with cochlear implants."
"The lower right quadrant, if it has anything in it, will be a “C”, to indicate that the butt side of the rivet is to be countersunk, (such as a double flush plug) for the NACA method (82 degrees, rather than the 100 degrees for under a manufactered head)."