Correct spelling, explanation: we spell habit with one consonant b because the word derives from Latin habitus meaning custom. Habbit is incorrect because spelling with double b.

Definition of habit:
1. noun, a custom, something we are used to doing, usual practice, may be positive or negative
She has a habit of waking up at 8 o’clock every day.
Jack had a bad habit of smoking.
2. noun, a long piece of clothing worn by monks or nuns
Mother Teresa’s habit was white and blue.

Idioms and phrases with habit:
→ to kick the habit, to give up a bad habit: The purpose of that organisation is to help drug addicts to kick the habit.
→ to get into the habit of doing something, to start to do something, to get used to a new habit: She got into the habit of healthy cooking really quickly.
My New Year’s resolution is to get into the habit of going to the gym regularly.

Incorrect spelling, explanation: because of its origin, the word habit should be spelled with only one b.