The most common and most likely answer to this crossword clue is the 13 letter word CONTAMINATION
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More clues leading to the result CONTAMINATION
Buddy explains!
The straight part
We know that "foreign matter" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case foreign matter = contamination.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 CONTAMINATION mean?
CONTAMINATION noun- The act or process of contaminating
- Something which contaminates.
- A process whereby words with related meanings come to have similar sounds.
- (etymology) The influence of one form (often from a foreign language) on the historical development of another form to which it may be related in meaning.
- The process of making a material or surface unclean or unsuited for its intended purpose, usually by the addition or attachment of undesirable foreign substances.