The word habit is typically used for personal actions – things that you do frequently
and repeatedly without even thinking about them:
▶️ I have the habit of falling asleep in front of the TV.
▶️ My brother has the bad habit of biting his nails.
▶️ Diana is trying to develop healthy eating habits.
▶️ I don’t trust him. He’s a habitual liar.
(the adjective form is “habitual”)
The word custom is used more for cultural or religious traditions.
▶️ People in this country have the custom of removing their shoes before
entering the house.
▶️ According to religious custom, wearing white symbolizes purity.
▶️ It’s customary to give people gifts on their birthdays.
(the adjective form is “customary”)
The word custom also has another meaning – as an adjective, it is the short form of
customized – meaning something is changed to make it more personal, individual,
or unique:
▶️ I got a custom cell phone case with a picture of my dog on it.