Scuba Pete
Le plongeur avec attitude...
From Dictionary.comBy those definitions, any opinon is a faith. Believing that Mint ice cream is the best ice cream is a faith, believing the truth that cats are adorable is a faith.
It's an extremely weak definition, and belief and faith are not interchangeable.
faith /feɪθ/ Pronunciation Key - Show Spelled Pronunciation[feyth] Pronunciation Key - Show IPA Pronunciation noun 1.confidence or trust in a person or thing: faith in another's ability. 2.belief that is not based on proof: He had faith that the hypothesis would be substantiated by fact. 3.belief in God or in the doctrines or teachings of religion: the firm faith of the Pilgrims. 4.belief in anything, as a code of ethics, standards of merit, etc.: to be of the same faith with someone concerning honesty. 5.a system of religious belief: the Christian faith; the Jewish faith.
I would suggest that atheism falls under 1, 2, 4 and 5. I am not sure why you see this as "weak", except as I pointed out, that you might have a rather dim opinion of faith due to religious inferences.