Solutions for Act II Scene 4 - Child-like

The first thing to notice is that the number of grinders matches the number of clues, and thus it should be obvious that the task at hand is to fill in the blanks under each grinder.

The next step is to realise that for each clue, the 'definition' is a word that ends in -ish, and that each of these words matches an 'adjective' - where (word)-like means you append -ish to the word that is being clued, much like what children might do if they lack the vocabulary to find the correct adjective. The first hint confirms this with (post-like -> pole-ish -> polish) and also indicates that it is allowable to drop the e when adding the suffix, which is a common feature of the English language.

Matching all the adjectives to the definitions reveals a cyclical grouping of words. Interpret groups as belonging to the same column and use word lengths to determine which column they belong in, and then read the letters that the arrows point to:

The letters indicated by the arrows spell out ONE FISH TWO FISH RED FISH BLUE FISH (A classic Dr. Seuss title, and of course, a children's book). We still haven't made use of the coloured arrows - the most intuitive thing to do is to spin the grinders so that the arrow points to a different letter on each word (barring the grinders without arrows, which don't need to be spun). But how many spaces should we turn them? The grey bars across the top connect the words RED with ONE and BLUE with TWO - after this, the last trick is to realise that RED+BLUE=PURPLE so the purple arrows correspond to a 3-space turn.

Spinning all the grinders and taking the new letters gives GRINDONFORMILESCROSSWILDSPACE. Searching this sentence reveals a line from Oh, The Places You'll Go! by Dr. Seuss, "and grind on for miles cross weirdish wild space." Thus the word missing from the quote is the solution, and weirdish is indeed how some might view the behaviour of children!

Design notes:
The first draft of this puzzle had clues that read much nicer, but when we discovered the Seuss quote with the perfect length and fitting answer we decided the clues could be a bit looser. Pairs such as ghoul-ghoulish and bull-bullish, and others where the definition was not a noun nor could be interpreted as a noun (like die) were included to satisfy the constraints needed to obtain weirdish as the answer. We tried to amend the niceness of the clues with semicolons for the less-nice clues, but as this was being done last-minute the call was made to simply release the puzzle rather than holding it back for such minor touch-ups. Apologies to anyone who really likes nice clues!

Many thanks to (the supreme leader) Sean Gardiner, who helped a lot with suggestions and amendments, found the Seuss quote and thematic answer, wrote a script to find usable words, and designed the visuals!

The answer is: weirdish