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I had a good long look through the Google Play store, and it looks like Google has really cracked down on "misleading apps" (even those that say outright that they record video).
Closest one I could find was https://play.google.com/store/apps/details?id=com.mahaya.application.hidden_camera which starts recording when you open the app, then when you tap the notification, it stops.
I haven't tried it myself, but that might work.
https://play.google.com/store/apps/details?id=com.waresoft.time is for photos, but is more discrete. It's a home screen widget that you place, and when you tap it, it takes photos.
Sorry I couldn't be more help. There used to be a million and one of these apps -- one actually looked like Apple's or Samsung's "Notes" app, and you could press in the right spot to start recording.
Maybe also ask in /r/androidapps and see if they know? Be upfront about why you want to record, otherwise they might shoo you away and assume you're in it for perverted reasons.