A diphthong refers to the phenomenon where two vowels are pronounced consecutively within a single syllable.

My account is protected by 2-step authentication.

He is doing a special exercise to train his digastric muscle.

He made a model of a dodecahedron.

This house is warm even in winter because it has double-pane windows.

He is learning how to use the second adjective.

Double dipping is a breach of etiquette.

This game is really fun from the second playthrough.

Redistribution of this software is prohibited.

The great icosihemidodecahedron is a cube with a very complex shape.