What do the words pea, cherry and sherry have in common? Each of these words is unnecessary. Each resulted from a mistake, a misunderstanding, a confusion of sounds.
At one time the English word for pea was pease, as in "pease porridge hot." The word was singular, but it sounded plural. And so pease became pea, the plural of which is now peas. What was the plural of pease? Presumably it was also pease. Some words, like sheep and fish, are the same in both singular and plural forms.
We got the words cherry and sherry in the same way. We got cherry from the French word cerise, which is singular but sounded plural to English speakers. So they invented the singular cherry, even though cerise itself is singular.
Sherry is a Spanish wine called Xeres, with the x pronounced with a sh sound. Again somebody thought this sounded plural, so in English it became sherry.
John McWhorter writes about how confusion over how words sound can lead to the creation of new words in his book What Language Is. He comments about how many young people now use all to mean said, as in "I'm all, 'What does that mean?'" He speculates that at some point in the future, this could conceivably lead to three new words in the English language: maw, raw and zaw. "I'm all" could become "I maw." "You're all" could become "you raw." "He's all" could become "he zaw."
"In the English of the distant future, speakers would have started hearing the sound before all as part of the word -- a perfectly natural process, after all -- and after a while people wouldn't even process the words as connected with all," McWhorter writes.
This may sound ridiculous, but at one time somebody probably thought the words pea, cherry and sherry sounded ridiculous, too.