Every time someone spells the word definItely, definAtely, somewhere, a fairy falls down, dead. Based on the number of times I've seen this misspelled on Facebook alone, we have the genocide of millions of tiny, winged creatures on our hands.
To make sure you never commit this atrocity again, let's first think about how you SAY the word. If someone asks you if Donald Trump would be a silly choice for President, which of the following is how your response would sound...
"definATely!" or "definITely!"......?
I really hope you chose the second option, because if not, then you sound like a dummy.
Define, definition, finite, infinite, infinitely, DEFINITE, DEFINITELY!
Notice how in all of the above similar words, there is not an A in sight. This is not coincidence. They share a root and have related meanings. Please don't use an A in any of these words ever again, for the love of all that is holy! Tinkerbell thanks you in advance for your cooperation. Now start clapping and chanting, "I do believe in fairies!" and maybe we can undo some damage.