1. (of letters) capital.
2. large, as either capital or uncial letters.
3. written in such letters ( opposed to minuscule).
4. a majuscule letter.
Personally, I am on a quest to introduce this word into the common slang as an adjective meaning superlative or spectacular.
The St. Louis Blues were majuscular in their game against the Sharks.
(From Agent of Byzantium.)