1
general::
Thrust in the edge of or end of something, such as bed linens or a shirt; also, make a child secure in bed by folding in the bedclothes. For example, Tuck in your shirt; it looks awful hanging out of your pants, or Mother went upstairs to tuck in the children. [First half of 1600s]
American Heritage Idioms
2
general::
Phrase(s): tuck someone in(to) something [and] tuck someone in
to place someone into something carefully; to wrap someone in blankets or something similar. • Father tucked Jimmy into bed an hour later than he should have. • Please tuck in Jimmy., Phrase(s): tuck something in(to) something [and] tuck something in
to fold or stuff something into something. • Please tuck your shirttail into your pants. • Tuck in your shirttail. • When you make the bed, you have to tuck the sheets in.
McGrawhill's American Idioms And Phrasal Verbs