A combining form usually signifying an instrument for viewing (with the eye) or observing (in any way); as in microscope, telescope, altoscope, anemoscope. [1913 Webster]

-scope, comb. form forming nouns denoting:
1 a device looked at or through (kaleidoscope; telescope).
2 an instrument for observing or showing (gyroscope; oscilloscope).

Derivative:
-scopic comb. form forming adjectives.

Etymology:
from or after mod.L -scopium f. Gk skopeo look at