A stiff hair. A stiff hairlike structure: the bristles of a wire brush. To stand stiffly on end like bristles: The hair on the dog's neck bristled. To raise the bristles: The cat bristled at the sight of the large dog. To react in an angry or offended manner: The author bristled at the suggestion of plagiarism. To be covered or thick with or as if with bristles: The path bristled with thorns. To cause to stand erect like bristles; stiffen. To furnish or supply with bristles. To make bristly; ruffle.