The name Adonijah is a combination of a couple of Hebrew terms: Adoni (meaning "my Master" Adonai) and Jah which is "Yah" because there is no J in the Hebrew alphabet. Thus the name can be rendered "My Master is Ahayah" or "Ahayah is my Master".
After the death of his elder brothers Amnon and Absalom, he became heir-apparent to the throne, but Solomon, a younger brother, was preferred to him. Adonijah, however, when his father was dying, caused himself to be proclaimed king. But the prophet Nathan and Bathsheba induced David to give orders that Solomon should immediately be proclaimed and admitted to the throne.
Adonijah fled and took refuge at the altar, receiving pardon for his conduct from Solomon on the condition that he showed himself "a worthy man" (1 Kings 1:5-53). He afterwards made a second attempt to gain the throne, by trying to marry David's last woman, Abishag from Shunem, but Solomon denied authorization for such an engagement, even though Bathsheba now pleaded on Adonijah's behalf. He was then seized and put to death (1 Kings 2:13-25).