Q. Hello! My question is regarding the following sentence.

Excel is a worksheet application that allows you to enter and, more importantly, manipulate data on worksheets.

One of our copyeditors believes we should omit the “ly” from “importantly,” because she was taught that it was improper. Personally I think that the omission of the “ly” makes the sentence sound awkward, but I’m very willing to make the change if she’s right. If so, I’d like to know why it’s improper, because I can’t seem to find a source that discusses this particular adverb. According to the dictionary we use (Webster’s Collegiate ), “importantly” is an adverb. If she’s right, is it because the “ly” is unnecessary (like “ir” in irregardless)? Or is it because of the word “more”?

A. I defer to the American Heritage Talking Dictionary (1995, CD-ROM):

Usage Note: Some critics have objected to the use of the phrase more importantly in place of more important as a means of introducing an assertion, as in More importantly, there is no party ready to step into the vacuum left by the Communists. But both forms are widely used by reputable writers, and there is no obvious reason for preferring one or the other. In an earlier survey the introductory use of more importantly was acceptable to half of the members of the Usage Panel.

. . . in part because I agree, but also because CMOS, as far as I know, doesn’t cover this issue. Perhaps more important, though, are those among my more venerable colleagues who disdain “more importantly.” (It is perhaps interesting to note that there is not one occurrence of importantly in the sixteenth edition of CMOS.)