I sometimes hear these nouns used interchangeably.
Problem:
These nouns are not all synonyms.
Explanation:
A “baluster” is a moulded shaft that most often supports the handrail of a staircase but also can be used to support the coping of a parapet, which is a wall-like barrier often at the edge of a roof.
The noun “baluster” comes from the Italian word — balaustra — for a pomegranate flower because the traditional shape of a baluster resembles the half-open pomegranate flower.
Balusters often are made of stone or wood and are sometimes made of metal.
A “balustrade” is a sequence of balusters that support a handrail.
A “banister” — also spelled with two “n”s — is another name for a staircase baluster, but many architects and interior designers prefer to reserve the word “banister” for a narrower, more-modern support.
Now here is where it becomes more confusing.
Many Americans — I cannot speak for other countries — also use the word “banister” to refer to the handrail of a staircase.
Solution:
- Use “baluster” to refer to a pomegranate-flower-shaped support of a staircase handrail.
- Use “balustrade” to refer to a sequence of balusters.
- Use “banister” to refer to a non-pomegranate-flower support of a staircase handrail.
- Be aware that some use “banister” also to refer to the staircase handrail itself.