To Be Transparent
To Be Clear, To Be See-through
intransitive verb, godan verb
This is a combination of the words 透ける and 通る. Something that is transparent enough for things (like light) to pass through it is still going to be transparent, aka to be see-through.
The readings for this word are both kun'yomi readings. You've learned both of these readings by now so you should be able to read this on your own.
彼女の手は透き通るほど白かった。
Her hand was so white it was almost transparent.
水が透き通っていてきれい。
The water is very clear and beautiful.
玉ねぎが透き通ってきたら肉を入れてください。
Once the onions become transparent, add the meat.