Learn Finnish: Uusi säännöstö on hyvin tiukka. - The new set of rules is very strict.

It is derived from the noun sääntö (rule). By adding the collective suffix -stö, the meaning becomes a 'set of rules' or 'regulations'. Because the base word contains the front vowels ä and ö, vowel harmony dictates that we use -stö instead of -sto.

Why does the nt in sääntö change to nn in säännöstö?

The collective suffix -sto or -stö usually attaches to the weak vowel stem of the word. Therefore, the strong consonant cluster nt in sääntö undergoes consonant gradation and weakens to nn to form säännöstö.

Hyvin usually means 'well'. Why is it translated as 'very' here?

While hyvin is the adverb form of hyvä (good) and means 'well', it is also one of the most common ways to say 'very' in standard Finnish when placed before an adjective. In spoken Finnish, you might also often hear tosi tiukka.

What other meanings does the adjective tiukka have besides 'strict'?

Besides describing rules, deadlines, or people as strict, tiukka is the standard word for 'tight' in a physical sense, such as tight clothing. It can also describe a tight or close situation, like an evenly matched sports game.