When it comes to making a noun plural, there are a few general rules we follow in English.
Most are are pretty easy. Slap an "s" on the end of "book" or "dog" or "desk" and suddenly you've got more than one. If the word ends with a vowel followed by a "y", the same rule applies, like "keys" and "boys."
If you've got a "y" preceded by a consonant, no sweat. Just trade out the last two letters for "ies" to get "cherries" or "babies" or "buddies."
There are other rules, and of course, they all have exceptions. But today we want to talk about pluralizing one word in particular: maître d'.