Incorrect spelling, explanation: although in Old English the word had been known as fullfyllan, in Middle English it was changed and spelled as fulfillen with one consonant l in the element ful. Nowadays, this element is often used as a suffix added to nouns to form adjectives, appearing at the end of the word. But in the words, fulfill and fulsome the element ful occurs at the beginning. There is no such word as fullfill and this form is incorrect.

Correct spelling, explanation: the word fulfill is not a compound verb because it consists of the forming element ful and the verb fill. The form was very similar in Middle English as fulfillen. It is interesting that the element ful is usually at the end of the word, for example, cheerful, dreadful, powerful. But in the word fulfill it occurs at the beginning. It is because fulfill is one of the survivors of Old English. Therefore, fulfill is a correct form, and fullfill does not exist and it can be a misspelling.

Correct spelling, form popular outside North America, correct also in Canada.

Definition of fulfill:
verb, to complete a task or duty; do what is required,
Next year I will go to Bulgaria and my dream will be fulfilled at last.
Sarah was disappointed because her daughter did not fulfill her promise of watering the plants.
You must fulfill your duty immediately.

Phrases with fulfill:
fulfill a need – provide something that someone needs,
Trains fulfill a need of people who do not have cars.
fulfill a wish – to make something come true,
Libby was excited to fulfill her husband’s wish of giving him this book.

Incorrect spelling

Incorrect spelling