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Occasionally

/əˈkeɪʒənəli/

Happening from time to time, not regularly or always.

Synonyms:

Men are crippled that way occasionally.

And though there were voices which occasionally said:

'Nothing at all, but I have met him occasionally.'

Derived from the Latin word occasionalis, from occasiō, meaning a happening or an opportunity, combined with -ally to convey frequency.

26 mentions per 1 million words

Often

Hint: Frequency according to COCA