Have you tried looking up these three words here?
1. May I know the relations between word, letter and alphabet?
2. Is alphabet a collection of letters according to what I searched from the old thread? Then how about a word?
any of a set of conventional symbols used in writing or printing a language, each symbol being associated with a group of phonetic values in the language; character of the alphabet
one of the units of speech or writing that native speakers of a language
usually regard as the smallest isolable meaningful element of the language, although linguists would analyse these further into morphemes related adjective lexical verbal
a set of letters or other signs used in a writing system, usually arranged in a fixed order, each letter or sign being used to represent one or sometimes more than one phoneme in the language being transcribed
Another letter: O
Another letter: R
Can you see the relationship now?
Yes, I do. Thank you.