From Longman Dictionary of Contemporary Englishbanisterban‧is‧ter /ˈbænɪstə $ -ər/ noun [countable] 
TBBa row of wooden posts with a bar along the top, that stops you from falling over the edge of stairs
TBBa row of wooden posts with a bar along the top, that stops you from falling over the edge of stairsExamples from the Corpus
banister• Shake the stair banisters and rail - are they loose?• He shot out a hand and caught the banister, steadying himself.• As I did so I grabbed the banister to save myself.• She grabbed the banister and dragged herself upwards.• He hugged the banister, counting its bar-like wooden rods until he reached the turn where it met the wall.• I went out naked on the landing and looked over the banisters.• Frankie stared through the banisters, willing the kitchen door to open.• Through his screams she heard voices, and went to the banisters.Origin banister (1600-1700) baluster “one of the sticks of a banister” ((17-21 centuries)), from French balustre, from Italian balaustro; → BALUSTRADE 