The most common and most likely answer to this crossword clue is the 9 letter word IMMERSION
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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 IMMERSION mean?
IMMERSION noun- The act of immersing or the condition of being immersed.
- An immersion heater.
- A smooth map whose differential is everywhere injective, related to the mathematical concept of an embedding.
- The disappearance of a celestial body, by passing either behind another, as in the occultation of a star, or into its shadow, as in the eclipse of a satellite.
- A form of foreign-language teaching where the language is used intensively to teach other subjects to a student.