The connection is a bit metaphorical. The bramble bush is known for its rough, prickly exterior, which is how the word came to be used to describe someone who is abrupt, blunt, or rough in manner.
Here's how the evolution likely played out:
1. "Bruscus" (Late Latin): Describing the prickly nature of the bramble bush.
2. "Brusque" (Old French): Evolved to describe a person with a prickly or rough personality.
3. "Brusque" (English): Borrowed from Old French and used to describe a person who is abrupt or blunt in manner.
So, while the word originally referred to a physical plant, it's metaphorical meaning developed over time to describe a person's personality trait.