In a way that depends on certain conditions being met; not absolutely or unconditionally.
From 'conditional' (from Latin 'conditio') plus the adverbial suffix '-ly'. It emerged in English around the 15th century as logic and philosophy became more sophisticated.
When someone says 'I'll conditionally agree to go to the party,' they mean yes, but only if specific things happen first—it's the linguistic way of saying 'it depends.'
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