The most common and most likely answer to this crossword clue is the 7 letter word GLEAMED
G
L
E
A
M
E
D
Buddy explains!
The straight part
We know that "What Eddystone did" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what eddystone did = gleamed.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 GLEAMED mean?
GLEAMED verb- To shine; to glitter; to glisten.
- To be briefly but strongly apparent.
- To disgorge filth, as a hawk.