that is to say

Related to that is to say: upmost, To Say the Least

that is to say

In other words; or, to clarify or explain more clearly. No, I have never met him—that is to say, we've never been formally introduced. I'll be there this afternoon. That is to say, after about four o'clock or so.
See also: say, that
Farlex Dictionary of Idioms.

that is to ˈsay

in other words: We’ll meet again three days from now, that is to say on Friday.
See also: say, that
Farlex Partner Idioms Dictionary

that is to say

In other words.
See also: say, that
American Heritage® Dictionary of the English Language, Fifth Edition.
See also:
  • that is
  • explain (oneself)
  • explain oneself
  • explain yourself
  • (all) dressed up
  • dressed up
  • dress up
  • dude oneself up
  • duded up
  • dooded