Please provide the specific idiom you would like me to analyze, and I can help explain its meaning.
dead
studied
Based on the context provided, the most likely meaning of the underlined word is "accident."
jailer
teeth
An idiom is a form of expression in a general group or culture. Something like 'It's raining buckets.' This doesn't mean there are literal buckets falling it just means it's raining hard. You most likely will have to define what each idiom means.
posture
nephew
the cave entrance
tree branches
fundamental principle
blood