You might have seen a pain scale in your doctor's office before. One common type shows a series of numbered cartoon faces moving from 0 (smiling and pain-free) to 10 (weeping in agony.) A doctor would ask a person in pain which face matched up with what they were feeling. They might seem simple.
In our day this might be more than one. For Israelite King Echov, one particular foreign wife, Isabel, was one too many. King David is said to have had eighteen wives and concubines, seven mentioned by name in the OT and the others mentioned in the oral tradition.
Who Were the Concubines? Apart from Sarah (mother of Isaac), and Hagar (mother of Ishmael), Abraham took to wife (after the death of Sarah) Keturah, and begat 16 descendants through her (Genesis 25:1-4). In addition a reference is made to the sons of the concubines, that Abraham had (Genesis 25:6). One explanation (Rashi) says that Keturah and the concubines are one and the same and that the word 'pilagshim' translated as 'concubines' should be read as in the singular. The text itself supports this explanation.