touch something—
1. put the hand or finger upon smth. so as to feel it:
- As his hand touched the surface of the mirror, it rippled like the water in a pond. He drew his hand back, startled.
2. (cause to) be in contact with smth.:
- Scientific information on the Martian atmosphere was gathered even before the Landers touched the surface.
3. have to do with smth.:
- I still find it hard to believe teachers would come to workshops and refuse to touch the computers.
touch upon something—mention smth. briefly, casually, or in passing:
- Himes succeeded in treating more extensively and intensively themes he had only touched upon in his first book.