Il rotore è meno costoso di quanto temevo.

In Italian, nouns are very often used with an article where English might omit it.

So il rotore means the rotor:

• il = the
• rotore = rotor

If you were speaking in a general or dictionary-like way, you might sometimes see the noun without the article, but in a normal sentence like this, il is the natural choice.

Also, rotore is a masculine singular noun, so il is the correct article.

È is the verb is from essere.

The accent is important because it distinguishes:

• è = is
• e = and

So:

• Il rotore è meno costoso... = The rotor is less expensive...
• Il rotore e... would mean The rotor and..., which would be wrong here.

Meno costoso means less expensive.

This is a standard comparative structure in Italian:

• meno = less
• adjective = the quality being compared

So:

• meno costoso = less expensive
• meno grande = less big / smaller
• meno difficile = less difficult

Here, costoso agrees with rotore, which is masculine singular, so the adjective stays in the masculine singular form.

Yes, often you could.

Both can express a similar idea:

• meno costoso = less expensive
• più economico = more economical / cheaper

But there is a slight difference in nuance:

• meno costoso focuses directly on cost
• più economico can sound a bit broader and sometimes more practical or stylistic

In this sentence, meno costoso is perfectly natural and very close to the English structure less expensive than I feared.

In this sentence, di quanto introduces the second part of a comparison.

The structure is:

• meno + adjective + di quanto + clause

So:

• meno costoso di quanto temevo = less expensive than I feared

You can think of di quanto here as meaning something like than what / than how much in a comparative sense, even though the natural English translation is simply than I feared.

This is a very common Italian pattern:

• È più difficile di quanto pensassi. = It’s more difficult than I thought.
• Costa meno di quanto immaginavo. = It costs less than I imagined.

Because Italian normally needs quanto in this kind of comparison.

After a comparative like meno costoso, you usually cannot directly put the clause by itself. The language uses di quanto to connect the comparison properly.

So:

• meno costoso di quanto temevo = correct
• meno costoso di temevo = incorrect

A good way to remember it is that Italian often uses di quanto where English simply uses than plus a clause.

Temevo is the imperfetto of temere.

The imperfect is used here because it describes a past mental state or ongoing attitude:

• temevo = I feared / I was afraid / I was worrying

This fits the idea of what you expected before finding out the actual cost.

If you said ho temuto, it would sound more like a completed event, which is less natural here. The sentence is not about one single moment of fear, but about your prior expectation.

So temevo works well because it means something like:

• than I had been fearing
• more naturally in English: than I feared

Literally, temere means to fear.

But in contexts like this, English often translates it more naturally as:

• to fear
• to worry
• to expect, unfortunately
• to be afraid that

So meno costoso di quanto temevo means literally:

• less expensive than I feared

But the sense is:

• less expensive than I was afraid it would be
• less expensive than I expected

This is a good example of how the most literal translation and the most natural translation are not always exactly the same.

Because in Italian, many adjectives commonly come after the noun, especially descriptive ones like costoso.

So:

• il rotore costoso = the expensive rotor

In this sentence, the adjective is part of the predicate after è:

• Il rotore è meno costoso...

That is completely normal in Italian and English:

• The rotor is less expensive

So there is nothing unusual here. Italian adjectives can sometimes come before the noun, but costoso is very naturally placed after it when directly modifying a noun, and here it appears after the verb because it is part of the statement about the rotor.

Not really in a natural English translation, even though quanto often relates to how much / how many / how.

In this sentence, quanto is part of the fixed comparative structure di quanto. So it is better to understand the whole chunk together.

A literal breakdown might suggest:

• less expensive than how much I feared

But that is not normal English. The natural translation is:

• less expensive than I feared

So yes, quanto has its usual idea of degree or amount, but in practice you should learn di quanto here as a comparison pattern.

Yes. A few natural alternatives are:

• Il rotore costa meno di quanto temevo.
  This focuses more directly on the price: The rotor costs less than I feared.

• Il rotore è meno caro di quanto temevo.
  Caro is another common word for expensive.

• Il rotore è meno costoso di quanto pensassi.
  This means less expensive than I thought, which is slightly less emotional than temevo.

The original sentence is perfectly natural, especially if you want to keep the idea of concern or worry.

Both can mean expensive, but there is a slight nuance:

• caro is very common in everyday speech
• costoso can sound a bit more formal, precise, or descriptive

So:

• È caro. = It’s expensive.
• È costoso. = It’s expensive / costly.

In many contexts they are interchangeable. In a sentence about a mechanical item like il rotore, costoso sounds quite natural and perhaps a little more technical or neutral.

It is basically neutral.

Nothing in it is especially informal or slangy, and nothing is highly formal either. It would fit well in:

• conversation
• writing
• technical discussion
• business context

The word rotore already gives it a somewhat technical feel because it refers to a specific object, but grammatically the sentence is standard everyday Italian.