In publishing, “TK” is the abbreviation for “to come.” When you are working on something and need to indicate where information you don’t yet have will go, you say “TK.” (For instance: “Joe Blow moved to Missoula from TK in 1984,” where TK means you need to find out where he moved from, and will insert the info at that spot when you get it.)
Why is this “TK” and not “TC”?
In my experience (11 years in publishing): the letter combination of “TK” almost never comes up in everyday English. “TK” stands out like a sore thumb. And, in modern times, computer searches grab it instantly.
Why originally? The first reason above, probably combined with the fact that the frequently encountered “TOC” (table of contents) was already taken and might be confused with “TC” if that were used.
Subeditor here… my understanding is that it’s from the deliberate misspelling “to kum”. Editors and proofreaders tend to deliberately misspell placeholder copy so that it stands out and cannot be mistaken for actual copy, e.g. I might write Hedliiine in heer plz.
This site agrees, although spells it “tokum”.
Thanks.
twicks, an editor-in-chief with 15 years’ experience 