The unstressed vowel in the word "frightening" is the letter "i" in the second syllable "-ten-".
The unstressed vowel in the word "poisonous" is the 'i' in the second syllable.
The unstressed vowel in the word "abandon" is the letter "a".
The unstressed vowel in the word "sentence" is the second "e" sound.
The unstressed letter in "frightening" is the second "i." It is pronounced quickly and with less emphasis compared to the other letters in the word.
An unstressed vowel is a vowel in the word you don't sound.
Frightening
An unstressed vowel is a vowel in the word you don't sound.
An unstressed vowel is a vowel in the word you don't sound.
An unstressed vowel is a vowel in the word you don't sound.
An unstressed vowel is a vowel in the word you don't sound.
e
The unstressed vowel in the word "boundary" is the letter "o" which is pronounced as /ə/ (schwa sound).
y
E
The unstressed vowel in the word "sentence" is the second "e" sound.
The unstressed vowel in the word "abandon" is the letter "a".
There are actually two unstressed vowels in the word "similar". The first vowel, "i" is the only stressed vowel. The other two reduce to schwa in speech.