Some very famous pieces of music have started with a mood description written on the sheet music by the composer.
Some other have become the perfect example of a given mood (Appassionata, Pathetic for Beethoven)
You could start with the MIREX vocabulary clusters
- Cluster 1: passionate, rousing, confident, boisterous, rowdy
- Cluster 2: rollicking, cheerful, fun, sweet, amiable/good natured
- Cluster 3: literate, poignant, wistful, bittersweet, autumnal, brooding
- Cluster 4: humorous, silly, campy, quirky, whimsical, witty, wry
- Cluster 5: aggressive, fiery, tense/anxious, intense, volatile,visceral
Some people use research from psychologist about human moods such as Robert Thayer's (not restricted to music).
Classifiying music is a very active research subject, especially these days for commercial reasons. Every internet music platform wants to propose and sell tracks to their users by different recommendation systems. Classifying (if possible automatically) music tracks becomes a way to feed such a recommendation system.
If people work with clusters, it is because they encountered difficulties in predicting reliably appartenance of music to finer divisions.
To refine these mood clusters, what you can do is take all the adjectives in each cluster, their synonyms and try to see if you can either group some of them or draw limits between them based on simple concepts.
Companies like Pandora are known to have designed a multi-criteria classification of music pieces and song, constructed first by humans as the Music Genome Project. Their model is quite sophisticated and could be of great interest to a composer.
Other usual (commercial) suspects (without restricting themselves to mood classification or contiguity) are Last.frm, MusicBrainz, Spotify, Musicovery, Aupeo, Stereomood, ... Members of these organizations sometimes write research articles about what they do. Many universities labs do research on this (US MIT, Sony, French IRCAM, ...). There are alternative systems, some based on color like Ghost.
Also if you want to have non standard descriptive phrase for music pieces, you can enjoy Satie's french humour, like in "Morceaux en forme de poire".