Crossword Genius

Quite an occasion when the extreme left write? (3-6,3)

Ross

I believe the answer is:

red-letter day

I'm a little stuck... Click here to teach me more about this clue!

'quite an occasion when the extreme' is the definition.
I can't tell whether this definition defines the answer.

'left write?' is the wordplay.
I cannot quite see how this works, but
'left' could be 'red' (red can informally mean communist) and 'red' is located in the answer.
'write?' could be 'letter' (lettering is a kind of writing) and 'letter' is present in the answer.
The remaining letters 'day' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for red-letter day that I've seen before include "Memorably important occasion" , "Noteworthy time" , "Memorable occasion" , "Momentous date" , "Special date in the calendar" .)

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.