Vashni - The true name of Samuel's first-born, which was "Joel" (see the margin and references), has here dropped out; and the word properly meaning "and his second (son)" has been taken as the name of the first.

The first-born Vashni, and Abiah - There is a great mistake in this verse: in 1-Samuel 8:2 we read, Now the name of his (Samuel's) first-born was Joel; and the name of his second Abiah. The word יואל Joel is lost out of the text in this place, and ושני vesheni, which signifies the second, and which refers to Abiah, is made here into a proper name. The Septuagint, Vulgate, and Chaldee, copy this blunder; but the Syriac and Arabic read as in 1-Samuel 8:2. The MSS. have all copied the corrupted Hebrew in this place. Jarchi labors to restore the true reading, and yet preserve the integrity of the text, by paraphrasing thus: "And the second, (ושני vesheni), in respect of the first, he was Abiah; and the second, in respect of Abiah, he was Joel."
These, Joel and Abiah, were the two sons of Samuel, who administered justice so badly that the people, being oppressed, began to murmur, and demanded a king. See 1-Samuel 8:1, etc.

And the sons of Samuel; the firstborn (e) Vashni, and Abiah.
(e) Who is also called Joel, (1-Samuel 8:2; 1-Chronicles 6:33).

the sons of Samuel--The sons of Samuel are here named Vashni and Abiah. The first-born is called Joel (1-Samuel 8:2); and this name is given to him in 1-Chronicles 6:33. It is now generally thought by the best critics that, through an error of the copyists, an omission has been made of the oldest son's name, and that Vashni, which is not the name of a person, merely signifies "and the second." This critical emendation of the text makes all clear, as well as consistent with other passages relating to the family of Samuel.