The first things we want to do here are identify the images and work out what the given words have to do with each other. Attempting either (or both) of these approaches should help confirm the puzzle's mechanic. We can note for instance that each pair of words (on either end of an arrow) have synonyms with similar letters (e.g. ALBUM/ALBUMEN; CHOOSE/CHEESE). We can also note that the images all depict things whose plurals are irregular (foot, goose, man, and mouse are the more obvious ones).
What we appear to want to do then is attach the images to the arrows in some way that relates the images' irregular plurals and the synonyms' similarities. The trick is to note that each "transformation" of one word into another (represented by the arrow) is a change to the end of the word modelled on the way one of the pictures pluralises. For instance, ALBUM would become ALBUMEN when pluralised if it behaved the same way as OX→OXEN, and CHOOSE becomes CHEESE when behaving like the pluralisation of GOOSE→GEESE. This idea is supported by the title, "Additions" loosely implying going from one to many, as well as the way most words change when pluralised.
All together we have:
Now the remaining piece of information we have not used is the letters attached to each image. Considering they should be placed in the squares on each arrow, we can now read the letters from left to right to get the message WORD ENDING. Note also that one picture has not been used, that of the MATRIX attached to the letter S.
The final step then is to put the matrix picture in the final, right-pointing arrow. Using the same pattern, this implies we want a word for "word ending" that looks like the word MATRIX and becomes a new word when "pluralised" the same way MATRIX is. There is only one compelling case: SUFFIX when pluralised like MATRIX gives SUFFICES, a new word. (Note that while "suffices" is an accepted plural of "suffix", "suffixes" is far more common, and "suffices" far more commonly means "satisfies or is adequate".) So we've thematically found an unrelated "pluralised" version of a word that refers to the theme of changing word endings.
The S on the final image was meant to further hint at the answer beginning with S, but also served the duty of pluralising the clue (WORD ENDINGS) and so tied into the theme in more ways than expected. While this did make the message discoverable simply by anagramming, it didn't particularly help with finding the answer, and we didn't mind if it did since this was a one-star puzzle and was intended to have multiple entry points.
|The answer is: suffices|