Deputy, n.; pl. Deputies.
Etymology: [F. député, fr. LL. deputatus. See Depute.]
1. One appointed as the substitue of another, and empowered to act for him, in his name or his behalf; a substitute in office; a lieutenant; a representative; a delegate; a vicegerent; as, the deputy of a prince, of a sheriff, of a township, etc. There was then [in the days of Jehoshaphat] no king in Edom; a deputy was king. 1 Kings xxii. 47. God's substitute, His deputy anointed in His sight. Shak.
Note: Deputy is used in combination with the names of various executive officers, to denote an assistant empowered to act in their name; as, deputy collector, deputy marshal, deputy sheriff.
2. A member of the Chamber of Deputies. [France] Chamber of Deputies, one of the two branches of the French legilative assembly; -- formerly called Corps Législatif. Its members, called deputies, are elected by the people voting in districts.
Syn. -- Substitute; representative; legate; delegate; envoy; agent; factor.
Shades of meaning
Fernald has no entry of its own for deputy; he lists it under delegate.
Where he writes about it:
In strict usage the deputy or delegate is more limited in functions and more closely bound by instructions than a representative. — from delegate
A single officer may have a deputy; many persons combine to choose a delegate or representative. — from delegate