Keturah

The wife of Abraham, after the death of Sarah, Genesis 25:1-6. Though she is called a "concubine," this may have been to distinguish her sons as well as Ishmael from Isaac the son of promise, Genesis 25:6; 1 Chronicles 1:32; Galatians 4:22,30. Her sons were the ancestors of many Arabian tribes.

Source: ATS Bible Dictionary
Keturah

Incense, the wife of Abraham, whom he married probably after Sarah's death (Genesis 25:1-6), by whom he had six sons, whom he sent away into the east country. Her nationality is unknown. She is styled "Abraham's concubine" (1 Chronicles 1:32). Through the offshoots of the Keturah line Abraham became the "father of many nations."

Source: Easton's Bible Dictionary
Keturah

(incense ), the wife of Abraham after the death of Sarah. (Genesis 25:1; 1 Chronicles 1:32) (B.C. 1860.)

Source: Smith's Bible Dictionary