1
general::
Also, touch upon. 1. Mention briefly or casually in passing, as in He barely touched on the subject of immigration. [First half of 1600s] 2. Approach closely, verge on, as in This frenzy touched on clinical insanity. [Early 1800s]
American Heritage Idioms
2
general::
Phrase(s): touch on something
Fig. to mention something; to talk about something briefly. • In tomorrow’s lecture I’d like to touch on the matter of taxation. • The teacher only touched on the subject. There wasn’t time to do more than that., Phrase(s): touch (up)on something
Fig. to mention something; to talk about something briefly. • In tomorrow’s lecture I’d like to touch on the matter of taxation. • The teacher only touched upon the subject. There wasn’t time to do more than that.
McGrawhill's American Idioms And Phrasal Verbs