Can iOS' builtin dictionary be accessed/browsed as an independent app?
There used to be a nice little app (that luckily I still have) that did exactly that: let you search for definitions directly. It was called Dictionary+ (link no longer available), Apple removed it reportedly for violating the UIReferenceLibraryViewController's terms of use, which states that it should not be used to display wordlists, create a standalone dictionary app, or republish the content in any form.
There's a replacement open source app that you can build, sign and install it manually, I haven't tried it, though: https://github.com/josh-/DictionaryPlusPlus
In recent iOS version you can also access definitions from the phone’s search (Spotlight) but for some reason sometimes it doesn’t work and may require internet.