From BiblePortal Wikipedia

Hastings' Dictionary of the Bible [1]

SHIMEATH . A name given to the father or mother of one of the murderers of Joash (  2 Kings 12:21 ,   2 Chronicles 24:26 ). The murderer himself is called Zabad in 2 Ch. and Jozacar in 2Kings. Probably for Zabad in 2 Ch. we ought to read Jehozabad , and undoubtedly Jozacar and Jehozabad are identical, and by scribal repetition (dittography) we have the two really identical names and the varying forms Shimeath , Shimrith , and Shomer . The descriptions ‘Ammonitess’ and ‘Moabitess’ in 2 Ch. are certainly later embellishments of the story, and Shimeath was probably the father of the one murderer, Jehozabad, and an Israelite. The Shimeathites were a family or division of the tribe of Caleb (  1 Chronicles 2:55 ). They may be included in the description ‘the families of the scribes, which dwelt at Jabez,’ but the whole passage leaves us uncertain. The Vulg. [Note: Vulgate.] regards the name as referring to the function of a section of the scribes ( resonantes ) after the Exile.

W. F. Boyd.

Smith's Bible Dictionary [2]

Shim'eath. (feminine of Shimeah ). An Ammonitess, mother of Jozachar or Zabad, one of the murderers of King Joash.  2 Kings 12:21;  2 Chronicles 24:26. (B.C. 809).

Morrish Bible Dictionary [3]

An Ammonitess, mother of Jozachar, or Zabad.  2 Kings 12:21;  2 Chronicles 24:26 .

Holman Bible Dictionary [4]

 2 Kings 12:21 2 Chronicles 24:26

Fausset's Bible Dictionary [5]

 2 Kings 12:21;  2 Chronicles 24:26.

International Standard Bible Encyclopedia [6]

shim´ḗ - ath ( שׁמעת , shim‛āth , or שׁמעת , shim‛ath  ; the Septuagint in 2 Kings, Ἰεμουάθ , Iemouáth , Codex Vaticanus in 2 Chronicles, Σαμά , Samá , Codex Alexandrinus Σαμάθ , Samáth , Lucian, Σαμαάθ , Samaáth ): Father of Jozacar (  2 Kings 12:21 (22)), one of the murderers of Joash, king of Judah. According to   2 Chronicles 24:26 Shimeath is an Ammonitess and the mother, not the father, of Jozacar. Many textual emendations have been suggested (compare HDB , article "Shimeath"), but they are unnecessary, as the Chronicler's revised version of the incident in Kings was a deliberate one. The Chronicler was a sturdy opponent of intermarriage, and in the story of the assassination of King Joash he saw an opportunity to strike a blow against the hated practice. In the older account in Kings the names of the conspirators are given as "Jozakar the son of שׁמעת , shim‛ath , and Jehozabad the son of שׁמר , shemer ." The two names are both masculine; but the final tāw ת of the former looked to the Chronicler like the feminine ending and offered him his opportunity. In his account, the one of the two murderers (dastardly villains, even though the king had merited death) was "the son of ( שׁמעת , shim‛ath ), the Ammonitess " and the other was "the son of (שׁמרית , shimrı̄th ), the Moabitess " (compare Torrey, Ezra Studies , 212 ff).