To smother is to overwhelm or suffocate. If you've ever had a boyfriend or girlfriend who calls you twenty five times an hour to check up on you, then you know what it means to be smothered by someone.
The word smother literally means to deprive of oxygen, so it can be used to refer to someone who gets suffocated by a pillow. In everyday conversation, the word is often used to refer to the act of making someone feel like they’re being deprived of oxygen or personal space. If you have a mother who likes to smother you by asking where you're going every time you see her, then it's likely you’re already dreaming of moving out!