Learn Polish: Ten samochód osobowy jest o metr węższy. - This passenger car is a meter narrower.

In Polish, when you want to express the margin of difference in a comparison (like 'a meter narrower' or 'two years older'), you must use the preposition o followed by the Accusative case. While English often drops the preposition (saying 'a meter narrower' instead of 'narrower by a meter'), Polish strictly requires o.

Since o takes the Accusative here for the margin of difference, shouldn't metr change its ending?

It is actually in the Accusative case! Because metr is a masculine inanimate noun, its Accusative form is exactly identical to its dictionary (Nominative) form. If the unit of measurement were a feminine noun, you would clearly see the ending change, for example: o jedną sekundę (by one second).

What is the base dictionary form of węższy?

The base adjective is wąski (narrow). To form the comparative, the -ski suffix is dropped, and the root undergoes a consonant mutation where the s changes to ż, before adding the comparative ending -szy. This makes wąski become węższy.

What does the word osobowy add to the meaning of samochód?