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to be transparent; to be see-through; to be clear
to be clear (of a voice or sound)
この湖の水は透き通っていて美しい。
The water in this lake is crystal clear and beautiful.
彼女の声は透き通っていてきれいだ。
Her voice is clear and beautiful.
透き通るような青空が広がっていた。
A crystal clear blue sky spread out.