Crossword puzzle clue "first code word"

First word across in the first-ever crossword (1913) and the first of a dozen appearances of the word in this puzzle's grid, written word search-style (left, right, down, and diagonally) ... Can you f

Secret code, in the secret code

Code hidden in a bar code

First code word

First radio code word?

Its postal code is the first two letters of the alphabet, good luck remembering that though

First radio code words

___ code (first three digits of a phone number)