acrophony

noun, plural a·croph·o·nies.

1. the use of what was originally a logogram as a phonetic symbol for the initial sound of the word the logogram represented, as, in Semitic writing, the use of a picture of a shepherd’s crook to represent the sound (l), the first sound of lamed, the Hebrew word for a shepherd’s crook.
2. the use of a word as the name of the alphabetical symbol representing the initial sound of that word.