The form is the predecessor of the crossword puzzle. Forms are simple geometric shapes filled with interlocking words reading across and down, or occasionally in other directions. Word squares are a common example of forms, but there are also half-squares, diamonds, hexagons, stars, and other shapes.
Often, the same words read in both directions in a form, and ones with different words in the two directions were called double forms.
An example form:
DIAMOND
1. You might get one "for effort"
2. Gorilla, for one
3. A fruit
4. A tree
5. You might get one "for effort"
Answer at end.
In the late 19th and early 20th century, these puzzles were quite popular. In 1913, Arthur Wynne created what has become known as the first crossword puzzle, though it was nothing more than a hollow diamond with a different numbering scheme to a formist. However, this puzzle, published in the New York World, led to other designs which quickly began to resemble the modern crossword puzzle more than the form.
These days, forms are still created in the National Puzzlers League but are otherwise nearly non-existent.
Answer to the above:
A
APE
APPLE
ELM
E