The term 'banister post' refers to a vertical post that supports a handrail, which is part of a staircase. The crossword solutions for this term are 'newel' (5 letters), 'RAIL' (4 letters), 'RAILING' (7 letters), and 'slid' (4 letters). Newel is a large post at the beginning or end of a banister, while RAIL is a horizontal bar that runs along the length of the banister. RAILING is the combination of posts and rails, and slid is a sloping piece of wood that connects the handrail to the stairs.