The most common and most likely answer to this crossword clue is the 6 letter word MONTHS
I've seen this crossword clue in The Guardian
M
O
N
T
H
S
More clues leading to the result MONTHS
Buddy explains!

The straight part
We know that "Parts of the year" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case parts of the year = months.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MONTHS mean?
MONTHS noun- A period into which a year is divided, historically based on the phases of the moon.
- A period of 30 days, 31 days, or some alternation thereof.
- (in the plural) A woman's period; menstrual discharge.
- A woman's period; menstrual discharge.