Endoscope is a modern scientific formation. Endo- supplies inside, and -scope supplies a viewing instrument: the name describes a way of seeing within the body.
The components have older Greek histories; the complete instrument name belongs to modern scientific vocabulary.
Sources
- Merriam-Webster: endoscope
Word History identifies scientific vocabulary; the explanatory note gives endo- as inside.
- Merriam-Webster: endo-
The combining-form section gives inside, Greek endon, and the endoskeleton example.
- Merriam-Webster: -scope
The noun combining-form definition and history supply a viewing instrument and Greek -skopion via New Latin -scopium.
- Online Etymology Dictionary: -scope
Also built on *-scope* "an instrument for seeing": microscope