Interlock
Two or more words or phrases are interlocked to form a longer one; unlike the alternade, the parts aren’t combined in a strict pattern. Example: ONE = fig, TWO = rebus, WHOLE = firebugs. The part whose first letter appears first in the longer word (fig in the example) is called ONE, and the other parts are numbered in the order their first letters appear.
The solution: COMPLETE = galoshes, ONE = gosh, TWO = ales.
All words in an interlock must in fact interlock. None may appear unbroken, as urn does in ONE = tome, TWO = urn, THREE = ant, WHOLE = tournament; this is not an acceptable base.
In a reversed interlock, after interlocking the parts, you reverse the result. The parts are numbered in the order that their first letters appear in the unreversed result. Example: ONE = late, TWO = circle, ALL = electrical.
Even with easy words in the base, the interlock can be difficult to solve because the letters can be combined in so many ways. In kindness to solvers, composers should be sure interlock parts are especially well clued.
The interlock was proposed as early as June 1945, but it caught on when Brutus introduced it in April 1977.