Defined: Orchestra

The origin and definition of words can change over time and have differing meanings. The word orchestra is an example of this. Orchestra as I typically use the word refers to a group of musicians playing together. Below is Merriam-Webster's definition of the word and a bit of its history.

Orchestra: Noun
Origin and Etymology:
Latin, from Greek orchēstra, , from orcheisthai to dance; perhaps akin to Sanskrit ṛghāyati he trembles, he rages.
First Known Use: 1606

Definition:

1a :  the circular space used by the chorus in front of the proscenium in an ancient Greek theater
b :  a corresponding semicircular space in a Roman theater used for seating important persons

2a :  the space in front of the stage in a modern theater that is used by an orchestra
b :  the forward section of seats on the main floor of a theaterc :  the main floor of a theater

3 :  a group of musicians including especially string players organized to perform ensemble music — compare band.

History of Orchestra
"In ancient Greek plays the chorus danced and sang in a space in front of the stage. The Greek name for this space was orchēstra, which came from the verb orcheisthai, “to dance.” The English word orchestra came from the Greek word for the space in front of a stage. At first the English word was used to refer to such a space but is now used to mean “the front part of the main floor.” In today's theaters a group of musicians often sits in the space in front of the stage. Such a group, too, came to be called an orchestra."


Source: https://www.merriam-webster.com/dictionary/orchestra