According to Genesis 25:1, Keturah is described as being Abraham’s wife:
“Abraham married another wife named Keturah.”
The word used for wife in the Hebrew is (‘ishshah) (Strong’s No. 802) and The Brown-Driver-Briggs Hebrew and English Lexicon (2001) defines the meaning of the word as “woman, wife, female”.
But according to I Chronicles 1:32, we are told that Keturah was Abraham’s concubine:
“Sons of Keturah, Abraham’s concubine: Zimran, Jokshan….”
The Hebrew used here according to the BDB lexicon is either (piylegesh) or (piyegesh) (Strong’s No. 6370) and the lexicon defines the meaning as “concubine”.
It is not possible for Keturah to be both a wife and concubine. The difference is without a doubt truly glaring, that one wonders what the missionary excuse will be for the above contradiction.
 James Strong, The New Strong’s Exhaustive Concordance of the Bible (Thomas Nelson, 1996)
 F Brown, S. Driver & C. Briggs, The Brown-Driver-Briggs Hebrew and English Lexicon (2001), p. 61
 James Strong, op. cit.
 F. Brown, S. Driver & C. Briggs, 0p. cit., p. 811