On a recent program we lamented the lack of a term for the cozy place behind a waterfall. In no time at all we heard from a fellow who proposed the term cascave.

You won't find cascave in any dictionary, since the word was coined by the children of our correspondent. Cascave fits (or should we say falls) into the linguistic category known as family words.

According to word-collector Paul Dickson, a family word is coined by (and used almost exclusively within) a family. Family words usually aren't written down, and only rarely do they become established in the general lexicon. One exception is googol, the name for the number one followed by 100 zeroes. That word comes from the nine year old nephew of American mathematician Edward Kasner.

Family words usually fill a specific need. The blend word milkstache is shorthand for a milk mustache. The acronym F.H.B. (for Family Hold Back!) is an unobtrusive way to enjoin family members to restrain themselves in front of guests when food is in short supply. The onomatopoeic nicknocks names automobile turn signals.

Occasionally, adults discover that what they consider family words, the rest of the world considers part of the general vocabulary. Such is the case with the terms mudroom, church key, and pie-eyed, all of which were reported to Dickson as family coinages.