From BiblePortal Wikipedia

Fausset's Bible Dictionary [1]

A station in Israel's march ( Numbers 33:18-19): from Rethem or Retem , the "broom"; KJV "juniper." The same encampment as that at Kadesh ( Numbers 13:26). Rithmah is a descriptive epithet, from the broom abounding there; probably applied to the encampment in this neighborhood in the first march toward Canaan, to distinguish it from the second encampment in the same district, but not the same spot, in the 40th year ( Numbers 33:36-38;  Numbers 13:21-26).

Morrish Bible Dictionary [2]

One of the stations of the Israelites.  Numbers 33:18,19 . By comparing this passage with  Numbers 11:35 and   Numbers 12:16 it appears that Rithmah is in the wilderness of Paran, and the passages refer to the first visit of the Israelites to that locality. See Wanderings Of The Israelites

Hawker's Poor Man's Concordance And Dictionary [3]

A place of encampment where Israel rested in the wilderness, ( Numbers 33:18) Probably the place abounded with juniper trees, since the name signifies juniper.

Smith's Bible Dictionary [4]

Rith'mah. (Heath). A march-station, in the wilderness,  Numbers 33:18-19, probably, northeast of Hazeroth.

Hastings' Dictionary of the Bible [5]

RITHMAH . A ‘station’ of the Israelites (  Numbers 33:18 f.).

Holman Bible Dictionary [6]

 Numbers 33:18-19

Easton's Bible Dictionary [7]

 Numbers 33:18,19

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [8]

(Heb. Rithmah', רַתְמָה , Heath ; Sept. ῾Ραθαμᾶ ), the seventeenth station of the Hebrews in the wilderness ( Numbers 33:18-19). About half a day's journey south from Wady Kiseima, (See Azmon) is found a valley called Wady Rithimath, or Wady Abu-Retemat. Rothem literally is a broom bush; hence Rithmah, the region of the Brush or Heath, and near this wady the broom bushes are abundant. So Schwarz ( Palest. p. 212), who identifies Rithmah with Kerdesh-Barnea. It probably lay immediately west of that place. (See Exode).

International Standard Bible Encyclopedia [9]

rith´ma ( רתמה , rithmāh , "broom"): A desert camp of the Israelites (  Numbers 33:18 ,  Numbers 33:19 ). The name refers to the white desert broom. See Wanderings Of Israel .