The most common and most likely answer to this crossword clue is the 3 plus 6 letter word AWE STRUCK
I've seen this crossword clue in The Daily Telegraph
A
W
E
S
T
R
U
C
K
Buddy explains!
The straight part
We know that "Lost for words" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lost for words = awe struck.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 AWE STRUCK mean?
AWE STRUCK adjective- Filled or overcome with awe or wonder.