What is the unstressed letter in frightening?

The unstressed letter in "frightening" is the e at the end of the word.

Here's why:

* Stress: The stress in "frightening" falls on the first syllable ("fright").

* Unstressed Vowels: Unstressed vowels often have a reduced sound, almost like a schwa (ə). In this case, the "e" at the end is silent.

So, while it's spelled "frightening," it's pronounced more like "fright-nin".