To be somewhat
silly or
goofy, while still having a certian amount of
sophistication; sort of like having a
mellowly
comical behavior. If you think of the humorous
frivolity of silly
inventions, such as
the works of
Rube Goldberg, you have discovered the
essence of 'whimsical'.
I found the other definitions here lacking in depth and only giving synonyms or a very brief sentence. If you look at the context it is frequently used in, the word 'whimsical' doesn't really have any direct synonyms. It has a meaning all it's own.