Correct spelling, explanation: the word tomorrow comes from Old English and its origins go back to the 13th century. First known as to morgen, on (the) morrow. The meaning of the word morrow is important here: it simply means morning and at first, today’s version was written as two words: to morrow (so: to morning). It was written like this until the 16th century and then with a dash (to-morrow) until the 20th century. Then it started to be written as one word and since there was a vowel and a consonant to join and it was completely pronounceable there was no need to double the m. therefore tomorrow is the correct modern form, and tommorrow is a misspelling.

Definition of tomorrow:
noun, the day after today
Are you going with us to the swimming pool tomorrow?
I can’t be at your party, I’m sorry but I have an important exam tomorrow.

Phrases with tomorrow:
as if there was no tomorrow – acting without thinking of consequence, carpe diem
She is very careless and acts as if there was no tomorrow.
better an egg today than a hen tomorrow – it is better to have something sure now than to wait for something better but unsure
I think you should take this job. Remember, better an egg today than a hen tomorrow!
jam tomorrow – a never-fulfilled promise
He promised jam tomorrow, but he didn’t keep it.
here today, gone tomorrow – an opportunity that lasts for a very short time
We tried to enjoy our career, because we knew that it’s here today, gone tomorrow.

Incorrect spelling, explanation: to understand why tommorrow is incorrect we need to go back to the origins of tomorrow, which is Old English to morrow (meaning to (the) morning). The word wasn’t written as one until the 20th century, but due to the nature of the sounds being joined, there was no reason to double the m. Therefore the correct form is tomorrow.

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling