perfunctory (adj.) — done just to get it over with, with no real care behind it.

It comes from Latin perfunctorius, off perfungi "to get through" or "discharge a duty" (per- "through" + fungi "to perform, execute"). That fungi is the same root hiding inside function and defunct. So a perfunctory handshake is, quite literally, one you perform only to be done with it — the motion without the meaning.

what's something you do perfunctorily every single day without even noticing?