Looking up and Inputing arbitrary unicode characters in console/terminal

I'm looking for a simple, generic way to input arbitrary unicode characters in a text document on the terminal(e.g. in a terminal editor). A basic method I can imagine is having a simple text(utf-8) file containing two columns, the character's name or description, and the character itself. Then I can have a simple script to lookup a character through this file, e.g. using dmenu or similar. Are there similar methods available that would take care of this for me? Otherwise where can I find such mappings(names, utf-8 value) for common unicode characters(e.g. smileys, greek characters, mathematical symbols)? This seems like such a basic common need yet I'm having difficulty finding simple solutions readily available. Thanks!