g vs alphabetic character

g and alphabetic character both are nouns.

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

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

g: the 7th letter of the Roman alphabet
alphabetic character: the conventional characters of the alphabet used to represent speech

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

g (noun)	alphabetic character (noun)
the 7th letter of the Roman alphabet	the conventional characters of the alphabet used to represent speech
a metric unit of weight equal to one thousandth of a kilogram
a unit of force equal to the force exerted by gravity; used to indicate the force to which a body is subjected when it is accelerated