Here's how it works:
* "Plenty" is the base word, meaning a large amount or quantity.
* "-ful" is a suffix that means "full of" or "characterized by."
Therefore, "plentiful" means full of plenty, indicating a large or abundant amount of something.
This suffix "-ful" is common in English and can be used to form adjectives from various nouns. Other examples include:
* Beautiful: Full of beauty
* Hopeful: Full of hope
* Wonderful: Full of wonder