Someone who joins in or interferes with something without being invited or having the right to do so.
From 'inter-' (between) and 'loper' (one who leaps, from Dutch 'loopen'). Originally referred to someone who jumped into a business deal illegally; evolved to mean any unwelcome outsider.
The word 'interloper' perfectly captures that awkward feeling when someone crashes a party or meddles in your business. Shakespeare used the term to describe characters who disrupted orderly situations—it's been expressing this idea for over 400 years!
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