The most common and most likely answer to this crossword clue is the 10 letter word TELESCOPIC
I've seen this crossword clue in The Times
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More clues leading to the result TELESCOPIC
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The straight part
We know that "long-sighted" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case long-sighted = telescopic.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 TELESCOPIC mean?
TELESCOPIC adjective- Pertaining to, or carried out by means of, a telescope.
- Seen by means of a telescope; only visible through a telescope.
- Capable of seeing distant objects; far-seeing.
- Able to be extended or retracted by the use of parts that slide over one another.
- Referring to parts being extended or retracted along coinciding axes (with or without direct contact between the parts).