noun pl. apparatus -·ra′·tus or apparatuses -·ra′·tuses

1. the instruments, materials, tools, etc. needed for a specific use
2. any complex device or machine for a specific use
3. Physiol. a set of organs having a specific function the digestive apparatus
4. the means or system by which something is kept in action or a desired result is obtained; organization the apparatus of government
5. the notes, indexes, glossaries, etc. of a scholarly edition of a text
   in full apparatus criticus apparatus crit′i·cus (krit′i kəs)

Etymology: L, a making ready, preparation < apparare < ad-, to + parare, prepare