The most common and most likely answer to this crossword clue is the 10 letter word MAINFRAMES
I've seen this crossword clue in The Daily Telegraph
M
A
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N
F
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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 MAINFRAMES mean?
MAINFRAMES noun- A large, powerful computer able to manage very many simultaneous tasks and communicate with very many connected terminals; used by large, complex organizations (such as banks and supermarkets) where continuously sustained operation is vital