To furnish or cover with whiskers; to give whiskers to someone.
From 'be-' plus 'whisker' (from Dutch 'wijsker' or related to 'whisk'). The prefix makes it an active verb—giving or adding whiskers.
The existence of 'bewhisker' shows that even facial hair growth was poetic enough in the 17th-18th centuries to get its own 'be-' verb—fashion and grooming inspired language innovation.
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