Correct spelling, explanation: the word awful, quite literally, means full of awe. Based on the pronunciation, and the fact that the ending e was silent, it’s omitted in awful. In English, the suffix -ful is popular in the word-formation of adjectives. And, of course, it’s based on the word full. At first, the suffix was spelled with a double L, however, it became shortened to -ful over time, and it’s the correct spelling now.

Definition of awful:
adjective
1. terrible, unpleasant
It was cold, rainy, and it looked like a storm is coming – in other words, awful weather for a barbecue.
2. very much (emphatic word, usually showcasing a negative aspect of something)
I have an awful lot to do today, so I won’t be able to go out and party.
adverb
1. an emphatic synonym for “very”, usually in a negative context
We had to wait an awfully long time in the queue before we entered.

Incorrect spelling, explanation: awful, the correct spelling, is based on the word awe and the suffix -ful. In the past, the suffix was spelled as full, but the form became shorter and lost one L. As of now, think about words such as beautiful or wonderful – they are always spelled with one L. The same goes for awful – despite the logical construction, awfull is simply incorrect.

Incorrect spelling