Dictionary.com Unabridged (v 1.1) -
plen·i·po·ten·ti·ar·y
Pronunciation[plen-uh-puh-ten-shee-er-ee, -shuh-ree] noun, plural -ar·ies, adjective
–noun 1. a person, esp. a diplomatic agent, invested with full power or authority to transact business on behalf of another.
–adjective 2. invested with full power or authority, as a diplomatic agent.
3. conferring or bestowing full power, as a commission.
4. absolute or full, as power.

[Origin: 1635–45; < ML plénipotentiarius. See plenipotent, -i-, -ary]
Dictionary.com Unabridged (v 1.1)
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2006.
American Heritage Dictionary - - Share This plen·i·po·ten·ti·ar·y (plen'?-p?-ten'she-er'e, -sh?-re) Pronunciation Key
adj. Invested with or conferring full powers: a plenipotentiary deputy.
n. pl. plen·i·po·ten·ti·ar·ies
A diplomatic agent, such as an ambassador, fully authorized to represent his or her government.
[Medieval Latin plenipotentiarius, from Late Latin plenipotens, plenipotent-, invested with full power : Latin plenus, full; see pel?-1 in Indo-European roots + Latin potens, powerful; see potent.]