From BiblePortal Wikipedia

Hastings' Dictionary of the Bible [1]

Geder . An unidentified Canaanitish town, whose king was amongst those conquered by Joshua (  Joshua 12:13 only). It is very probably identical with Beth-gader of   1 Chronicles 2:51 . In   1 Chronicles 27:28 Baal-hanan, who had charge of David’s olives and sycomores, is called the Gederite , which may be a gentilic name derived from Geder, although some prefer to derive it from Gederah (wh. see).

American Tract Society Bible Dictionary [2]

The word signifies a wall, inclosure, fortified place; as do also the two names following, which are derived from it. Geder itself was an ancient Canaanitish place, in the plain of Judah,  Joshua 12:13 , and was probably the same with the following Gederah.

Fausset's Bible Dictionary [3]

One of the 31 kings defeated by Joshua W. of Jordan ( Joshua 12:13). In the extreme S. Possibly the Simeonite Gedor ( 1 Chronicles 4:39).

Holman Bible Dictionary [4]

 Joshua 12:13 1 Chronicles 27:28  Joshua 12:1

Morrish Bible Dictionary [5]

City in the south of Palestine, the king of which was slain by Joshua.  Joshua 12:13 .

Easton's Bible Dictionary [6]

 Joshua 12:13

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [7]

(Heb. id. גֶּדֶר , Sept. Γάδερ ), a name signifying a Wall (e.g. of a court, garden, sheepfold, etc., Proverbs 24, 31;  Ezekiel 42:10), hence an enclosed or fortified place, and thus the basis of several names of castellated towns (e.g. Gederah, Gedor, Gadara, Gederoth, etc.); used once only ( Joshua 12:13) in this simple form as that of one of the thirty- one ancient royal towns of the Canaanites, whose kings were defeated by Joshua. It is mentioned between Debir and Hormah; but, as the localities in that list are not strictly in geographical order, it may be identified with the GEDOR (See Gedor) (q.v.) in the mountains of Judah ( Joshua 15:58), and with the BETH-GADER (See Beth-Gader) (q.v.) of  1 Chronicles 2:51. The notices of Schwarz (Palest. pages 86, 104) are quite confused.

International Standard Bible Encyclopedia [8]

gē´dẽr ( גּדר , gedher ): A royal city of the Canaanites taken by Joshua along with Lachish, Eglon, Gezer, Debir and Hormah (  Joshua 12:13 f). It may be the city called "Beth-gader" in   1 Chronicles 2:51 , and the birthplace of Baal-hanan, who had charge of David's olives and sycamores ( 1 Chronicles 27:28 ); unidentified.

Kitto's Popular Cyclopedia of Biblial Literature [9]

Ge´der. This word signifies a wall, enclosure, or fortified place, and must be understood in this sense in the ensuing names. Geder itself was the name of an ancient town of the Canaanites, in the plain country of Judah , and was perhaps the same as Gederah.