A fechadura de que precisamos custa pouco, mas o senhorio ainda não a comprou.

Because the verb precisar is normally followed by de in standard Portuguese when it means to need.

• precisar de alguma coisa = to need something

So:

• Precisamos da fechadura = We need the lock.
• When that noun becomes part of a relative clause, the preposition must stay:
  • A fechadura de que precisamos = The lock that we need

English often drops the preposition, but Portuguese usually cannot do that here.

In standard European Portuguese, that is generally considered incorrect with precisar, because de is required.

The correct forms are:

• A fechadura de que precisamos
• A fechadura da qual precisamos (more formal)

So de que is the normal, natural choice here.

De que is a combination of:

• de = the preposition required by precisar
• que = the relative word meaning that / which

So the structure is:

• A fechadura = the lock
• de que precisamos = that we need

Literally, you can think of it as:

• the lock of which we have need

That sounds unnatural in English, but it helps explain why de is there.

A is the feminine singular definite article, meaning the.

• o = the, masculine singular
• a = the, feminine singular

Since fechadura is feminine, it takes a:

• a fechadura = the lock

This article is not the object pronoun a later in the sentence. They are two different words that just happen to look the same.

In European Portuguese, o senhorio means the landlord.

This is a very common Portugal Portuguese word. In Brazilian Portuguese, learners may more often encounter:

• o proprietário = the owner
• o dono = the owner
• o locador = the lessor, more formal/legal

If you are learning European Portuguese, senhorio is the natural everyday word for landlord.

Because senhorio is a masculine singular noun, so it takes the masculine singular definite article o:

• o senhorio = the landlord

Compare:

• a senhoria = the landlady

Portuguese uses articles more regularly than English, so the landlord is naturally o senhorio.

Ainda não means not yet.

So:

• o senhorio ainda não a comprou = the landlord hasn’t bought it yet

Depending on context, ainda não can sometimes feel like still hasn’t, but not yet is the most direct meaning here.

Examples:

• Ainda não cheguei. = I haven’t arrived yet.
• Ainda não sei. = I don’t know yet.

Here, a is a direct object pronoun meaning it.

It refers back to a fechadura, which is feminine singular. Because fechadura is feminine, the pronoun is a.

Object pronouns in Portuguese agree with the noun they replace:

• o = him / it, masculine singular
• a = her / it, feminine singular
• os = them, masculine plural
• as = them, feminine plural

So:

• comprou a fechadura = bought the lock
• comprou-a = bought it

But because of negation, the pronoun goes before the verb here:

• não a comprou

Because não triggers proclisis, which means the object pronoun comes before the verb.

So:

• Comprou-a. = He bought it.
• Não a comprou. = He didn’t buy it.

In European Portuguese, several words can force this before-the-verb position, and não is one of the most important ones.

So after negation, não a comprou is the correct order.

No. That is not correct here.

Since não triggers proclisis, the pronoun must come before the verb:

• ainda não a comprou ✅
• ainda não comprou-a ❌

Without a trigger like não, enclisis is often possible in European Portuguese:

• comprou-a = bought it

But with não, you need:

• não a comprou

Because the sentence is describing two different time relationships:

• de que precisamos = what we need now
• ainda não a comprou = he still hasn’t bought it up to now

So:

• precisamos is present tense: we need
• comprou is simple past, but with ainda não it often corresponds to English hasn’t bought yet

This is very common in Portuguese. Where English often uses the present perfect, Portuguese frequently uses the simple past with words like já or ainda não.

Compare:

• Já comprei. = I’ve already bought it.
• Ainda não comprei. = I haven’t bought it yet.

Custar means to cost, so custa pouco literally means costs little or more naturally is inexpensive / doesn’t cost much.

• A fechadura custa pouco. = The lock doesn’t cost much.

This is a very natural way to talk about price in Portuguese.

You could also say:

• A fechadura é barata. = The lock is cheap.

Both are correct, but custa pouco focuses on the amount of money, while é barata uses an adjective.

Because pouco here is being used adverbially, meaning little / not much.

• custa pouco = costs little / doesn’t cost much

If you said custa um pouco, that would usually mean costs a little, which can sound different in nuance and often less natural in this exact context.

So for it’s cheap / it doesn’t cost much, custa pouco is the normal phrase.

Yes. Both are grammatically correct:

• A fechadura de que precisamos
• A fechadura da qual precisamos

However, de que is usually more common and more natural in everyday speech and writing.
Da qual sounds a bit more formal or heavier.

For most learners, de que is the best choice here.

Several words would change to match the gender.

For example, with cadeado (padlock), which is masculine:

• O cadeado de que precisamos custa pouco, mas o senhorio ainda não o comprou.

Notice the changes:

• a fechadura → o cadeado
• object pronoun a → o

This is a good reminder that articles and object pronouns in Portuguese must agree with the noun’s gender.

Yes, mainly because of senhorio, which is characteristically European Portuguese for landlord.

The grammar of the sentence itself is standard and would be understood elsewhere, especially:

• de que precisamos
• ainda não a comprou

But the vocabulary choice senhorio strongly points to Portugal Portuguese.