The most common and most likely answer to this crossword clue is the 5 letter word GAPED
I've seen this crossword clue in The Daily Telegraph
G
A
P
E
D
More clues leading to the result GAPED
- Looked stunned as thong finally taken off
- Doctor penning article: editor looked astonished
- Looked astonished: leader of Greece to copy Germany
- On punching good daughter, primate looked amazed
- Opened wide? Good – dentist to start on filling with a drill
- Blank, news boss stared stupidly
- Midway through grooming, ape daintily yawned
- Was clearly surprised being space captain on paper
- Showed open-mouthed wonder seeing space-man?
- Space-man yawned
Buddy explains!

The straight part
We know that "stared stupidly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stared stupidly = gaped.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 GAPED mean?
GAPED verb- To open the mouth wide, especially involuntarily, as in a yawn, anger, or surprise.
- To stare in wonder.
- To open wide; to display a gap.
- Of a cat: to open the passage to the vomeronasal organ, analogous to the flehming in other animals.