Final answer:
The 'ay' in say, play, and tray is a suffix, which is a group of letters added to the end of a word to change its meaning or function.
Step-by-step explanation:
In the words say, play, and tray, the 'ay' combination of letters can be referred to as a suffix. A suffix is a letter or group of letters added to the end of a word to alter its meaning or function. In these particular words, 'ay' is serving as a vowel pattern or a phonogram that creates the long 'a' sound, which appears at the end of each word. It is a common linguistic phenomenon where two vowel sounds merge to form a unique sound, contributing to the richness and diversity of the English language's pronunciation patterns.