Catchword and Key word

Catchword noun - A word printed at the top of the page of a dictionary or other reference book to indicate the first or last item on that page.

Key word and catchword are semantically related. In some cases you can replace phrase "Key word" with "Catchword", this terms are similar.

Key word noun - A significant word used in indexing or cataloging.

Catchword and key word are semantically related. Sometimes you can use "Catchword" instead a noun phrase "Key word".