In dictionaries, glossaries and similar materials words are always organized alphabetically, which means each of them is organized according to the order of letters in an alphabet that in the English language means from A to Z. Additionally, it is common to find in this material guide words which are words printed in the top of the pages to show which is the first word in the page and the last word on it (following the alphabetical order).
This implies if the guide words are "signify" and "silly" in this page only words that in the alphabetical order are between these words would appear which means words such as silence, silent and also silk would appear, while others such as "sibling" and "signal" would be found in previous pages and words such as "slit" would be found in subsequent pages. Therefore, the word that would appear between these guide words is "Silk" as in terms of alphabetical order this goes between "signify" and "silly".