a thing that is added to something else to improve or complete it

an extra separate section, often in the form of a magazine, that is sold with a newspaper

the Sunday colour supplements

Our special supplement is packed with ideas for healthy hair.

a book or a section at the end of a book that gives extra information or deals with a special subject

the supplement to the Oxford English Dictionary

You can use these books as supplements to the basic English course.

an amount of money that you pay for an extra service or item, especially in addition to the basic cost of a holiday

There is a £10 supplement for a single room.

There is a supplement on rooms with a sea view.

Safety deposit boxes are available at a supplement.

to add something to something in order to improve it or make it more complete

LEARNit Dictionary