Joku piilotti vihjeen.

Because vihjeen is the object of the sentence, and here it is a singular total object.

In Joku piilotti vihjeen, the action is understood as completed: someone hid the whole clue / one clue completely. In Finnish, that often makes the object take a form that looks like the genitive singular, which is why vihje becomes vihjeen.

Compare:

• Joku piilotti vihjeen = someone hid the clue / a clue completely
• Joku piilotti vihjettä = someone was hiding a clue, or hid some clue in a more ongoing/incomplete sense

So the -n here signals a completed, whole object.

The dictionary forms are:

• joku = someone
• piilottaa = to hide
• vihje = clue, hint

In the sentence:

• joku stays as it is
• piilotti is the past tense form of piilottaa
• vihjeen is the object form of vihje

Piilotti is in the simple past tense (called the imperfect in Finnish grammar).

So:

• piilottaa = to hide
• piilotti = hid

This tells you the action happened in the past.

Because the subject is joku, which means someone and is grammatically singular.

In Finnish, the verb agrees with the subject:

• minä piilotin = I hid
• sinä piilotit = you hid
• hän piilotti = he/she hid
• joku piilotti = someone hid

Even though joku is indefinite, it still behaves like a singular subject.

Joku usually means someone or somebody. It refers to an unspecified person.

It is very common and neutral. It does not sound especially formal or especially casual.

For example:

• Joku soitti. = Someone called.
• Joku piilotti vihjeen. = Someone hid the clue.

So yes, it often has the feeling of some unknown person.

Because Finnish usually does not leave a direct object in its plain dictionary form in a sentence like this.

The dictionary form vihje is the nominative. But here the noun is functioning as an object, and because the action is complete, Finnish uses the total object form:

• dictionary form: vihje
• object here: vihjeen

So vihje is the base form, but vihjeen is the grammatically correct form in this sentence.

No. The correct verb here is piilottaa, not piilota or piilota/piilosi in that sense.

There are two related verbs that learners often mix up:

• piilottaa = to hide something
• piiloutua = to hide oneself, to hide, to go into hiding

So:

• Joku piilotti vihjeen. = Someone hid the clue.
• Joku piiloutui. = Someone hid / went into hiding.

If there is a direct object like vihjeen, you need piilottaa.

Yes. Finnish word order is fairly flexible, although the neutral order here is:

• Joku piilotti vihjeen.

You can change the order for emphasis:

• Vihjeen piilotti joku. = It was the clue that someone hid / Someone hid the clue.
• Piilotti joku vihjeen? = Did someone hide the clue? (in a certain context or style)

Even though word order can change, the case ending -n on vihjeen still helps show its role as the object.

So the original sentence is the most neutral and straightforward version.

It can mean either, depending on context.

Finnish does not have articles like a and the, so vihjeen by itself does not tell you which one to choose in English. The context decides:

• someone hid a clue
• someone hid the clue

If the listener already knows which clue is being talked about, English will usually use the clue. If it is new information, English may use a clue.

This is an important Finnish object difference.

• vihjeen = total object
• vihjettä = partial object

In many basic situations:

• Joku piilotti vihjeen. = Someone hid the clue / a clue completely.
• Joku piilotti vihjettä. = Someone was hiding a clue, or the action is viewed as incomplete/ongoing.

The exact contrast can depend on context, but a good beginner rule is:

• -n form → whole/completed object
• -ä/-ta form → partial, ongoing, incomplete, or indefinite amount

A simple pronunciation guide is:

• joku ≈ YO-ku
• piilotti ≈ PEE-loht-tee
• vihjeen ≈ VIH-hyehn

A few useful points:

• j in Finnish sounds like English y
• ii is a long vowel, so pii- is held a little longer
• hj in vihjeen can feel unusual to English speakers; it is roughly like vih-ye-
• stress in Finnish normally falls on the first syllable of each word:
  • JO-ku
  • PII-lot-ti
  • VIH-jeen

More or less yes, but it helps to learn it as a verb pattern.

The verb is:

• piilottaa = to hide

Its past form is:

• piilotti = hid

This follows a common Finnish verb change where the stem changes in the past tense. For a learner, the most useful thing is to memorize:

• piilottaa → piilotti

and then later learn the full conjugation pattern:

• minä piilotin
• sinä piilotit
• hän piilotti
• me piilotimme
• te piilotitte
• he piilottivat

So it is a normal Finnish verb pattern, even if it does not look completely transparent at first.