Here are some synonyms for "poorly understood":
* Unclear
* Ambiguous
* Mysterious
* Obscure
* Vague
* Insufficiently explained
* Not well-defined
* Lacking in understanding
Examples:
* "The causes of climate change are still poorly understood."
* "The relationship between the two species is poorly understood, but it appears to be symbiotic."
* "The ancient text was written in a language that is poorly understood by modern scholars."
In essence, "poorly understood" signifies that there is a gap in knowledge or a lack of definitive answers about something.