a cave: a natural hollow in rock large enough for a person to enter
This is the ordinary Hebrew word for a cave, a natural opening in a hillside or rock face that people could walk into and use. Every occurrence points to the same physical thing; the word does not shift its meaning from place to place.
What changes is what the cave is used for, and the Bible puts caves to a handful of practical uses. Some are burial places, above all the cave at Machpelah that Abraham buys to bury Sarah and where the family patriarchs are later laid to rest. Many more are places to hide: Lot and his daughters shelter in one, David and his men hide from Saul in the cave at Adullam and the cave at En-gedi, Obadiah hides a hundred prophets from Jezebel in caves, Elijah lodges in a cave at Horeb, and frightened Israelites flee into caves in the hills when an enemy overwhelms them.
The same word can be turned to a figure of speech. When Jeremiah calls the temple a cave used by robbers, he is picturing a cave as the kind of hideout a band of thieves would slip into between raids. The word itself still just means cave; the sting is in the comparison.
Because the sense never really varies, English can render it with the single plain word cave almost everywhere, only occasionally reaching for den when the cave is imagined as a haunt or hideout.