Kitto's Popular Cyclopedia of Biblial Literature
Ab, (father) is found as the first member of several compound Hebrew proper names—such as Abner, father of light; Abiezer, father of help; etc.By a process which it is not difficult to conceive, the idea of a natural father became modified into that of author, cause, source (as when it is said, 'has the rain a father?'—Job 38:28). So that, in course of time, the original meaning was so far modified that the word was sometimes applied to a woman, as in Abigail, father of joy.
Ab is the Chaldee name of that month which is the fifth of the ecclesiastical and eleventh of the civil year of the Jews. It commenced with the new moon of our August, and always had 30 days. This month is preeminent in the Jewish calendar as the period of the most signal national calamities. The 1st is memorable for the death of Aaron (Numbers 33:38). The 9th is the date assigned to the following events:—the declaration that no one then adult, except Joshua and Caleb, should enter into the Promised Land (Numbers 14:30); the destruction of the first Temple by Nebuchadnezzar (to these first two 'the fast of the fifth month,' in Zechariah 7:5; Zechariah 8:19, is supposed to refer); the destruction of the second Temple by Titus; the devastation of the city Bettar, and the slaughter of Ben Cozîbah (Bar Cocâb), and of several thousand Jews there; and the plowing up of the foundations of the Temple by Turnus Rufus—the two last of which happened in the time of Hadrian.
The 9th of the month is observed by the Jews as a fast, in commemoration of the destruction of the first Temple: the 15th is the day appointed for the festival of the wood-offering, in which the wood for the burnt-offering was stored up in the court of the Temple: to which Nehemiah alludes in Nehemiah 10:34, and Nehemiah 13:31. Lastly, the 18th is a fast in the memory of the western lamp going out in the Temple in the time of Ahaz (2 Chronicles 29:7, where the extinction of the lamps is mentioned as a part of Ahaz's attempts to suppress the Temple service). For an inquiry into what is meant by the western or evening lamp, see the article Candlestick.
Kitto, John, ed. Entry for 'Ab'. "Kitto's Popular Cyclopedia of Biblial Literature". https://www.studylight.org/encyclopedias/eng/kbe/a/ab.html.