A person who is skilled with both hands, or historically, a dishonest person who plays both sides against each other.
From Latin 'ambi-' (both) plus 'dexter' (right hand, skilled). The word literally means 'both-handed,' but in medieval English it developed a negative meaning referring to double-dealers and untrustworthy people.
Medieval English speakers used 'ambidexter' as an insult meaning someone who could work for either side untrustfully—it's fascinating because it shows how the same skill (using both hands) was seen as suspicious and dishonest by people who didn't understand that some people are just naturally ambidextrous.
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