Synonyms for Peephole:

n.

doorstep, doorstop, doorbell, doorjamb, doorknob, doorpost, door, slot, arch, doorplate, slit, crevice, doorknocker. artifact (noun)
spyhole.
peephole (noun)
spyhole, slot, slit, crevice.

Other synonyms:

Other relevant words:
slit, slot, crevice.