Synonyms of that is to say in English:

that is to say


See definition of that is (or that is to say)

phrase

1‘people emigrated for economic reasons—that is to say, because they were poor’

SYNONYMS
in other words, to put it another way, to rephrase it
i.e., that is, to wit, viz., namely, sc.
id est, scilicet, videlicet