The word cavity

I looked up the word cavity;
And found it had nothing to do with capacity;
I wanted to know if cavity had gravity;
I was asked if research was my daily activity;
That I should look up the word in its totality,
If I wanted to get to my research finality;
My efforts brought me back to cavity.
I looked at the whole matter and saw its density;
A could not deny the reality;
And what’s most important its complexity.