1. A power of attorney document given by shareholders of a corporation authorizing a specific vote on their behalf at a corporate meeting.
2. The function or power of someone who is authorized to act as the deputy or substitute for another person.
3. Etymology: from about 1440, prokecye, "agency of one who acts instead of another"; contraction of Anglo-French procuracie, from Middle Latin procuratia, "administration"; from Latin procuratio, "care, management" from procurare, "to manage".

Relating to something that is used in place of another thing: Jim arranged to have a proxy writer to compose contents for his website.

Sam's elderly mother arranged to have him be her proxy voter in the next city election.

To function as a substitute for another person or thing: Jake went to the fitness studio where he was proxying as a trainer in place of the regular one who was ill.