At one time the Greek word "elemental spirits", STOICHEIA meant the alphabet, "A,B,C..." By extension "A,B,C..." came to mean "the ABCs"; the ABCs of anything at all. The ABCs of baseball are the most basic aspects of baseball, the first principles, the rudiments -- as with sewing or music-making or arithmetic. The ABCs are the basic information about anything, the elements of anything, the sort of thing children learn in elementary school.
Meanings in Philo
4 Elements
That which has been created
Forces of Nature
Letters of the Alphabet
The basic sounds of speech
The Vowels
The Alphabet itself
The source of number
A constituent part of something
Elementary (opposite of completed)
Elemental (having a state of existence)
Idiomatic expressions