delta vs alphabetic character

delta and alphabetic character both are nouns.

Word	Noun	Adjective	Verb	Adverb
delta	Yes	No	No	No
alphabetic character	Yes	No	No	No

As nouns, alphabetic character is a hypernym of delta; that is, alphabetic character is a word with a broader meaning than delta:

delta: the 4th letter of the Greek alphabet
alphabetic character: the conventional characters of the alphabet used to represent speech

Other hypernyms of delta include letter, letter of the alphabet.

delta (noun)	alphabetic character (noun)
the 4th letter of the Greek alphabet	the conventional characters of the alphabet used to represent speech
a low triangular area of alluvial deposits where a river divides before entering a larger body of water
an object shaped like an equilateral triangle