The most common and most likely answer to this crossword clue is the 10 letter word LIGHTHOUSE
I've seen this crossword clue in The Times
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More clues leading to the result LIGHTHOUSE
- One providing warning via illuminating point?
- Flasher on the coast amusing those at theatre
- Flasher shocking South Leigh
- Amusing part of the zodiac is one that provides guidance for those at sea
- ———- shines and the lough is lit up
- Guide for sailors with happy hearts on river
- Is the ghoul, perhaps, a warning to mariners?
- Aid for maritime safety easily carried by legislative body
- No resistance to cavalry getting uniform replacement — it sends a warning
- Insect with inwardly broken thigh — it stands tall and bright
Buddy explains!

The straight part
We know that "Flasher on the coast" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case flasher on the coast = lighthouse.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 LIGHTHOUSE mean?
LIGHTHOUSE noun- A tower or other structure exhibiting a light or lights to warn or guide sailors.