The most common and most likely answer to this crossword clue is the 8 letter word BLISSFUL
I've seen this crossword clue in The Daily Telegraph
B
L
I
S
S
F
U
L
Buddy explains!

The straight part
We know that "Ecstatic" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ecstatic = blissful.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 BLISSFUL mean?
BLISSFUL adjective- Extremely happy; full of joy; experiencing, indicating, causing, or characterized by bliss.
- Blessed; glorified.