Well, according to wikipedia, which is usually fairly good w/ nomenclature-

In modern Arabic, the name Barack (Arabic: باراك ) pronounced ba'-rak, means "he who is blessed" or simply "blessed". A more common form in most Arabic-speaking countries is the passive Mubarak.

The usage of the root B-R-K as a male name meaning "blessing" occurs in the Ancient Semitic Sabean (barqac), in Palmyrene (baraq), and in Punic (Barcas, as surname of Hamilcar), and as a Divine name in Assyrian Ramman-Birqu and Gibil-Birqu[1], and personal Biblical name Barukh or Baruch (which is also the modern Hebrew cognate; see Book of Baruch for an instance of the name). "Barack" and "Baruch" are equivalent to "Benedict" (Latin Benedictus).


From the same source-

Sidney or Sydney was originally an English surname. Its main origin is from Old English words meaning "wide well-watered land". [1] It is generally conceded (without enthusiasm) that Sidney may also be a contraction of the French place name Saint-Denis, the Patron Saint of France, which was brought to England by the Normans. Hanks & Hodges point out that there is little evidence to support this derivation and it may be the result of folk etymology [2]. Reaney & Wilson state that "The name is usually derived from St. Denis (Normandy) but proof is lacking". [1]

In (Norman) French, Saint Denis (itself a contraction of Dionysius) would be pronounced something like "S' Deni'", which in England became "Sidney" through the folk etymology process when the Plantagenets became English.

The Dionysus ref is kinda funny.