I just found out that what I used to slide down was not a bannister (which is a family
name), and not even a banister. It was a baluster, or balustrade.
baluster - 1602, from It. balaustro (see balustrade).
balustrade - 1644, from Fr., from It. balaustro "pillar," from
balausta "flower of the wild pomegranate," from Gk.
balaustion. Staircase uprights had lyre-like double curves,
like the calyx tube of the pomegranate flower

hmm. m-w shows

Main Entry: ban.is.ter
Pronunciation: 'ba-n&s-t&r
Function: noun
Etymology: alteration of baluster
Date: 1641
1 a : a handrail with its supporting posts b : HANDRAIL
2 : BALUSTER 2
- ban.is.tered /-t&rd/ adjective

and baluster as:

Main Entry: bal.us.ter
Pronunciation: 'ba-l&-st&r
Function: noun
Etymology: French balustre, from Italian balaustro, from balaustra wild pomegranate flower, from Latin balaustium, from Greek balaustion; from its shape
Date: 1602
1 : an object or vertical member (as the leg of a table, a round in a chair back, or the stem of a glass) having a vaselike or turned outline
2 : an upright often vase-shaped support for a rail


so, it looks to me as if you did slide down the banister. sliding down a baluster would probably be very painful, unless you like that sort of thing.

And take note of the Italian word in wwh's paste: "baslustro" meaning "column." There's some more verticality for you!

sliding down a baluster would probably be very painful, unless you like that sort of thing

Remember Tom Lehrer's song (Bright College Days) which contained the line

"...soon we'll be sliding down the razor blade of life..."
Saw a cartoon in an old MAD illustrating the same thought...