Please answer the following question: Question: "__ first appeared in the Maitri Upanisad."  Context: "In the language of the Noble Eightfold Path, samyaksamādhi is "right concentration". The primary means of cultivating samādhi is meditation. Upon development of samādhi, one's mind becomes purified of defilement, calm, tranquil, and luminous."  Answer:
A:
samādhi