Answer:
'tri'
Step-by-step explanation:
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The apostrophe before the following syllable indicates that the previous syllable is stressed.
From LawlessEnglish.com "Syllable Stress "
English words that are polysyllabic (have more than one syllable) always have one syllable that is stressed. In most English dictionaries, the stressed syllable is indicated by a stress mark, a symbol that resembles an apostrophe. The stress mark follows the syllable that is stressed.
For example, in the word incredible, the second syllable (-cred-) is stressed. Here are some examples.
2 3 4
ex′it op′po·site Feb′ru·ar·y
hu′mid ex·am′ine in·cred′i·ble
ma·chine′ em·ploy·ee′ psy·cho′lo·gy
Here is the Dictionary.com for retribution retribution noun
ret·ri·bu·tion | \ ˌre-trə-ˈbyü-shən \
The apostrophe is before the 'byu so the PREVIOUS syllable is the one that is stressed.