This is the 846th most frequent Finnish word.
joulukuuta
"Joulukuuta" means "of December" in English.
Here, 'joulukuun' is the genitive case of 'joulukuu', indicating possession or relations, in this case, identifying 'the start of December' as the time referenced.
Joulukuun alussa on aina kylmää.
At the beginning of December, it is always cold.
Here, 'joulukuu' is used in its nominative singular form, representing the subject of the sentence and specifying the month as a general concept.
Joulukuu on vuoden viimeinen kuukausi.
December is the last month of the year.
In this sentence, 'joulukuuta' specifies the month of December in a genitive singular form, part of a date construction that describes this day.