ABC (n.)

"letters of a language arranged in customary order," 1570s, from Late Latin alphabetum (Tertullian), from Greek alphabetos, from alpha + beta.

It also is attested from early 15c. in a sense of "learning or lore acquired through reading." Words for it in Old English included stæfræw, literally "row of letters," stæfrof "array of letters," and compare ABC.

It was a wise though a lazy cleric whom Luther mentions in his "Table Talk,"—the monk who, instead of reciting his breviary, used to run over the alphabet and then say, "O my God, take this alphabet, and put it together how you will." [William S. Walsh, "Handy-Book of Literary Curiosities," 1892]

Alphabet soup is attested by 1907.

"primer, alphabet table," mid-15c., from Medieval Latin abecedarium "an ABC book," neuter of adjective abecedarius, used as a noun, from the first four letters of the Latin alphabet. Abecedarian (adj.) is attested from 1660s.