To tuck something is to put it in or under something else. This word is often used with the preposition "in."
Children like it when their parents tuck them in at night before they go to sleep.
Bobby can’t go to sleep unless his mother tucks him in.
When wearing a suit, a man should make sure his shirt is tucked in.
It’s fashionable nowadays to leave your shirt untucked (for a man), but sometimes it just looks sloppy.
"Tuck in your shirt!" said the teacher to the student.*
A turtle tucks its head and legs under its shell when it senses danger.
A duck tucks its head beneath its wings when it is sleeping.
When making a bed, the sheets might be tucked in under the mattress.
Boxes have flaps that are tucked in in order to keep the food fresh.
A cabin can be tucked away in a part of a forest that few people ever visit.
Tucked away inside a cave you might find bats and other animals.
He’s tucked in beneath a blanket.
Note: In the United States, at schools with a uniform policy, a teacher may tell a student to tuck in his shirt, but most schools are casual when it comes to clothing. A parent, however, will tell a child to tuck in his shirt if he is to be dressed for a formal occassion.)
