variant spelling of "banister" (one "n") - the handrail on a staircase.
Usage: "Bannister" (two "n"s) is probably the instinctive spelling, and almost certainly by far the more commonplace for names and places. (E.g., Sir Roger Bannister, the first sub-four-minute miler.) But the dictionaries say "banister" for the railing.
Link to this page: