The Collaborative International Dictionary of English v.0.48:

Maranatha \Mar`a*nath"a\, n. [Aramaic m[=a]ran ath[=a].]
   "Our Lord cometh;" -- an expression used by St. Paul at the
   conclusion of his first Epistle to the Corinthians (xvi. 22).
   This word has been used in anathematizing persons for great
   crimes; as much as to say, "May the Lord come quickly to take
   vengeance of thy crimes." See Anathema maranatha, under
   Anathema.
   [1913 Webster]

Easton's 1897 Bible Dictionary:

Maranatha
   (1 Cor. 16:22) consists of two Aramean words, Maran'athah,
   meaning, "our Lord comes," or is "coming." If the latter
   interpretation is adopted, the meaning of the phrase is, "Our
   Lord is coming, and he will judge those who have set him at
   nought." (Comp. Phil. 4:5; James 5:8, 9.)


Hitchcock's Bible Names Dictionary (late 1800's):

Maranatha, the Lord is coming