It's the stressed syllable in a word, the one you say a bit more forcefully than the others. In the word "tomorrow", you emphasize the syllable "mor" more than the other syllables.
Arthropathy is accented on the second syllable.
The first syllable is accented.
Verdict is accented on the first syllable.
The first syllable is accented.
second accented syllable
The second syllable is accented.
The second syllable is accented.
The first syllable is accented.
The first syllable is accented.
First syllable is accented.
ANSWER FOR is the accented syllable in formidable.
The accented syllable in "fountain" is the first syllable, "foun-".