Papilledema (or papilloedema) is optic disc swelling that is caused by increased intracranial pressure. The swelling is usually bilateral and can occur over a period of hours to weeks.[
Welcome to the mondofacto forum and thanks for the definition suggestion.
The UK spelling of papilloedema is included in the dictionary (http://www.mondofacto.com/facts/dictionary?query=papilloedema&action=lookup), but it is not re-directing to the definition when you search for the US version - papilledema, so you didn't find it. Thanks for alerting us to this, we will fix the problem as soon as possible.
Please let us know if you discover any other missing definitions.
Quick update: we've fixed the problem. A search for papilledema will now redirect you to papilloedema and a definition.
We are working on sorting out any teething-troubles with the US/UK redirect function, so please let us know if you come across any other problems of this nature.