In Geocaching.com you can search for caches starting with a particular piece of text. This is in Play / Hide and Seek a Cache.
Project-GC has more flexibility. Go to Home / Dashboard. In the wildcard search there you can search for a full word by entering it complete, or a partial word by surrounding it in asterisks. eg *ac* will find "cache", "bach" etc. Click the question mark there for more details.