Learn Portuguese (Portugal): O avião é menos perigoso do que o carro. - The airplane is less dangerous than the car.

We use the word menos (less) before the adjective, followed by do que (than). In this sentence, that gives us menos perigoso do que (less dangerous than).

Is it possible to drop the do and just say menos perigoso que?

Yes! When making comparisons with adjectives, do que and que are completely interchangeable. You can say menos perigoso do que o carro or menos perigoso que o carro. Both are common and mean exactly the same thing.

Why does the adjective perigoso end in an "o"?

Adjectives need to match the noun they are describing. Here, perigoso (dangerous) describes o avião (the airplane), which is a masculine noun. If we were describing a feminine noun like a mota (the motorcycle), we would use the feminine form perigosa.

Why do we say do que o carro instead of just do que carro?

In Portuguese, you usually need to include the definite article (o, a, os, or as) before the second noun in a comparison. So we literally say "than the car" (do que o carro).