[GregBuchholz]

Are you aware of '*' and '#', and 'gd'?

http://vim.wikia.com/wiki/Go_to_definition_using_g

[sillysaurus3]

It never seems to work for me. If I put the cursor over a word and type gd, it seems to go to the first line that the word is mentioned, not necessarily the definition. It's handy, for sure, but not too reliable. I think it can be improved with some plugins though.

[egjerlow]

These only work if your definition is in the same file, though.