UNIX style search syntax is supported. White space acts as an AND operator, while a single pipe (|) character acts as an OR operator. Use "ify$" to search for words that end in "ify", like "certify" and "classify". For full search syntax, see this reference.
This dictionary tool uses scanned PDFs of dictionaries, which were printed in the 20th century. Words that are common now may not have been common enough to be put into the dictionary back then. For example, the usage of the word "hello" has risen tremendously in the last 50 years (see graph).
I used OCR to do text detection on the dictionary images, and then built a web application with React to make it searchable. The code is open source