AMG: All Music Guide: Music Glossary
- Arrangements, Forms, and Structure
- Composition and Harmony
- Effects, Embellishments and Ornaments
- Recording, Processing, Sessions and Sound
- Vocal Performance, People, Technique
- Beat, Meter, Rhythm, and Tempo
- Ensembles, Combos, Groups and Bands
- Pitch, Notation, Mensuration and Dynamics
Creative Online Music Dictionary of Musical Terms
hnh.com: The Classical Music Website: Online Music Glossary
!FORTISIMO! Music Dictionary
Mysheetmusic Online Music Dictionary
This site lists online dictionaries in almost every language under the sun,
could come in handy for those Norwegian and Scandinavian pieces of music.
Sony/W.W. Norton: Essentials of Music: Online Glossary
Spindrift Thesaurus of Musical Terms
This archive of musical terminology gets special mention.
It's the only online reference I've found with the definition of "con islancio".