Questions & Answers about 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