baluster
Concise Oxford English Dictionary © 2008 Oxford University Press:
baluster /ˈbaləstə/
▶noun a short pillar forming part of a series supporting a rail or coping.
– origin C17: from Fr. balustre, from Ital. balaustro, from balaust(r)a ‘wild pomegranate flower’ (because of the resemblance to the curving calyx tube of the flower).
'baluster' also found in these Oxford entries:

