Dictionary.net

• ad-ul'am-[=i]t, adj. an inhabitant of Adullam, where was a cave to which flocked from all sides to David in exile men in debt, distress, or discontent (1 Sam. xxii. 1, 2). The name was applied by John Bright in 1866 to a Whig secession from the Liberal party.

1908 - Chambers's Twentieth Century Dictionary of the English Language
By Thomas Davidson

• M. P. seceding from Liberal Party in 1866.

1919 - The concise Oxford dictionary of current English
By Sir Augustus Henry