My friend's last name is Dopp.

The Dopps are a famous band from the 90s.

I packed my Dopp kit with all my toiletries for the trip.

I packed my Dopp kits for the trip.

I packed my dopp kit for the trip.

I packed my dopp kits for the trip.

I saw my doppelgänger at the mall yesterday.

I saw my doppelganger walking down the street.

The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source.

I ordered a doppio espresso at the coffee shop.