The most common and most likely answer to this crossword clue is the 10 letter word DEDUCTIONS
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Buddy explains!

The straight part
We know that "Markdowns" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case markdowns = deductions.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 DEDUCTIONS mean?
DEDUCTIONS noun- That which is deducted; that which is subtracted or removed
- A sum that can be removed from tax calculations; something that is written off
- A process of reasoning that moves from the general to the specific, in which a conclusion follows necessarily from the premises presented, so that the conclusion cannot be false if the premises are true.
- A conclusion; that which is deduced, concluded or figured out
- The ability or skill to deduce or figure out; the power of reason