An antonym of a word has the opposite meaning. So, an antonym of dangerous would be safe.
pulse what makes sence in the word
Reaction
aversion
"Following the impulse, he rushed after the car"
The Enterprise was on on impulse power only.
Patient
Planned
The word that means a fanciful notion or impulse is whimor whimsy. An antonym for whimsy would be seriousness or deliberation.
If you stick to items on your grocery list, you'll avoid impulse purchases.
Her impulse to shop was starting to take over her whole life. Another good sentence would be, she had a sudden impulse to buy the expensive purse.
The word has a short I, a short U, and a silent E.