mirror, speculum, barrel-head, round rice-cake offering
鏡 centers on a reflective surface that shows an image: a mirror. The extended meanings of speculum, barrel-head, and round rice-cake offering all share the idea of a smooth, round, reflective object.
鏡 combines 金 (metal) with 竟, which likely contributes the sound and the idea of a boundary or end, suggesting a polished metal surface that reflects an image.
The left side 金 (metal) and the right side 竟 (which looks like a stand with a shiny top) together suggest a polished metal mirror standing upright.
For キョウ, imagine looking into a mirror and seeing a giant 'K' staring back at you: K -> キョウ, and the mirror reflects the letter clearly.
mirror; looking-glass
glasses; eyeglasses; spectacles
microscope
telescope
binoculars; field glasses
kaleidoscope
mirror surface; lens surface
periscope
reading (farsighted) glasses; spectacles for the aged
reflective water surface; reflecting water
kagami mochi; New Year offering consisting of two mochi stacked on each other with a bitter orange on top, cut and eaten on January 11
magnifying glass; magnifier; loupe
magnifying glass
coloured glasses; tinted glasses; sunglasses
hand-mirror
polished mirror; clear mirror
bronze mirror
clear and serene (as a polished mirror and still water)
ancient triangular-rimmed mirror decorated with gods and animals
panel; scene-panel