The definition of habit is something that you do regularly, or an addiction.
Brushing your teeth every morning and every night is an example of a good habit.
Being addicted to heroin is an example of having a heroin habit.
Another usage for the noun Habit:Noun
1. Obsolete costume; dress
- a particular costume showing rank, status, etc.; specif., - a distinctive religious costume: a monk's habit
- a costume worn for certain occasions: a riding Habit
Origin of the word habit
Middle English ; from Old French ; from Classical Latin habitus, condition, appearance, dress ; from past participle of habere, to have, hold ; from Indo-European base an unverified form ghabh-, to grasp, take from source give transitive verb to dress; clothe