the.com/bannister
The handrail saving you from gravity, and every kid's preferred shortcut down.
means The railing along a staircase, plus the row of upright posts holding it up.
from A mangling of baluster, the slim pillar shaped like a half-open pomegranate flower; medieval craftsmen slurred it into banister, then doubled the n for good measure.
Spelling fightOne n is older; two n's won anyway.
Flower rootsBaluster comes from balaustion, wild pomegranate blossom.
Strict grammarBanister is one post; baluster is the whole set.