The most common and most likely answer to this crossword clue is the 13 letter word ACCLIMATISING
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The straight part
We know that "Getting used to" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case getting used to = acclimatising.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 ACCLIMATISING mean?
ACCLIMATISING verb- To get used to a new climate.
- To make used to a new climate or one that is different from that which is natural; to inure or habituate to other circumstances; to adapt to the peculiarities of a foreign or strange climate.