Η πρόληψη αποβλήτων είναι σημαντική.

A word-by-word breakdown is:

• Η = the
• πρόληψη = prevention
• αποβλήτων = of waste / of wastes / waste in a technical or general sense
• είναι = is
• σημαντική = important

So the structure is basically:

The prevention of waste is important
or more naturally in English, Waste prevention is important.

Η is the feminine singular definite article, meaning the.

It is used because πρόληψη is:

• singular
• feminine
• the subject of the sentence

So:

• η πρόληψη = the prevention

Greek uses definite articles more often than English in many contexts, so seeing η here is very normal.

Greek nouns have grammatical gender, and πρόληψη happens to be feminine.

You usually learn a noun together with its article:

• η πρόληψη = the prevention

A useful pattern: many nouns ending in -η or -ση / -ψη are feminine, including:

• η σκέψη = thought
• η χρήση = use
• η πρόληψη = prevention

Because πρόληψη is feminine, words that agree with it, like adjectives, also appear in the feminine form.

Because after πρόληψη we need a form meaning of waste, and Greek usually expresses that with the genitive.

So:

• απόβλητα = waste as a nominative/accusative plural form
• αποβλήτων = of waste / of wastes = genitive plural

This is similar to English prevention of waste.

So:

• πρόληψη αποβλήτων = prevention of waste

This kind of noun + genitive structure is very common in Greek.

Good question. You could say:

• η πρόληψη αποβλήτων
• η πρόληψη των αποβλήτων

Both are possible, but they are not used in exactly the same way.

η πρόληψη αποβλήτων is a very common general/technical expression, almost like waste prevention as a category or field.

η πρόληψη των αποβλήτων is more explicitly the prevention of the waste or of wastes, and can sound a bit more specific or more fully expanded.

In formal, environmental, or policy language, Greek often omits the article in this kind of genitive phrase.

πρόληψη is in the nominative singular because it is the subject of the sentence.

The basic pattern is:

• [subject] + είναι + [adjective]

So here:

• Η πρόληψη αποβλήτων = the subject
• είναι = is
• σημαντική = important

Because σημαντική is an adjective describing πρόληψη, and Greek adjectives must agree with the noun they describe in gender, number, and case.

Since πρόληψη is:

• feminine
• singular
• nominative

the adjective must also be:

• feminine
• singular
• nominative

That is why we get:

• σημαντικός = masculine
• σημαντική = feminine
• σημαντικό = neuter

Here the correct form is σημαντική.

Because in this sentence σημαντική is not directly inside the noun phrase. It is a predicate adjective, linked to the subject by είναι.

Compare:

• η σημαντική πρόληψη = the important prevention
  Here the adjective is directly attached to the noun.

• η πρόληψη είναι σημαντική = prevention is important
  Here the adjective comes after είναι and describes the subject.

So σημαντική is after είναι because the sentence means is important, not the important prevention.

είναι is the present-tense form of to be used for he/she/it and also for they in Modern Greek.

Here the subject η πρόληψη is singular, so είναι means is.

Examples:

• Η πρόληψη είναι σημαντική. = Prevention is important.
• Οι δράσεις είναι σημαντικές. = The actions are important.

Notice that είναι stays the same in both sentences. Greek does not distinguish is and are with different present-tense forms here; both use είναι.

A rough pronunciation is:

ee PRO-lee-psee a-pov-LEE-ton EE-ne si-man-dee-KEE

A more careful guide:

• Η = ee
• πρόληψη = PRO-lee-psee
• αποβλήτων = a-pov-LEE-ton
• είναι = EE-ne
• σημαντική = si-man-dee-KEE

A few helpful sound notes:

• β in Modern Greek sounds like v, not English b
• η, ι, υ, ει, οι often sound like ee
• ψ sounds like ps

The stress falls where the accent marks are:

• πρόληψη → stress on πρό
• αποβλήτων → stress on βλή
• είναι → stress on εί
• σημαντική → stress on the last syllable κή

Greek accent marks show which syllable is stressed, and they are very important for correct pronunciation.

Also note:

• Even if a word begins with a capital letter, the accent is still normally written: Η πρόληψη
• In all-caps writing, accents are often omitted, but in normal writing they stay

Yes, Greek word order is more flexible than English, but not every version sounds equally natural.

The neutral, standard order is:

Η πρόληψη αποβλήτων είναι σημαντική.

You might also see:

• Σημαντική είναι η πρόληψη αποβλήτων.
  = Important is waste prevention / Waste prevention is what is important
  This gives extra emphasis to σημαντική.

So yes, the order can change, but the original sentence is the most neutral and natural for straightforward statement style.

Yes, it is very common in environmental and policy language.

It works much like an English compound expression such as:

• waste prevention
• waste management
• pollution control

Greek often uses:

• a head noun first
• then a genitive noun

So:

• πρόληψη αποβλήτων = waste prevention
• διαχείριση αποβλήτων = waste management

This is a very useful pattern to recognize in formal Greek.

You could, and grammatically it reflects the Greek structure fairly closely. But in natural English, Waste prevention is important is usually the best translation.

So:

• Literal-ish: The prevention of waste is important
• Natural English: Waste prevention is important

Greek often uses a structure that sounds a bit more formal if translated word-for-word into English.