The most common and most likely answer to this crossword clue is the 8 letter word HERALDRY
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Buddy explains!

The straight part
We know that "Genealogical science" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case genealogical science = heraldry.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 HERALDRY mean?
HERALDRY noun- The profession or art of devising, granting and blazoning coats of arms, tracing genealogies and ruling on questions of protocol or rank.
- An armorial ensign along with its history and description.
- Pageantry.