The project below has a single blank sprite whose scripting area holds nine one-line example scripts, built from word blocks like last letter of and all but last letter of (already loaded for you from Snap!'s "Words, sentences" library) along with join and list contains. Start by trying each expression with different inputs until you can say what it does in general, not just for the example input.

Then build a plural reporter block that takes a noun as input and reports its correctly spelled plural: "day" → "days", "boss" → "bosses", "butterfly" → "butterflies". Start with the simple add-an-"s" rule, hunt for words it gets wrong, and add cases (words ending in "s", "x", consonant + "y", …) until it handles your whole test list. Keep your test words in a Snap! list, and use map and keep to test plural against all of them at once.

Your work autosaves (and you can use the Save button); earlier versions are available from the Revisions dropdown.