1. impossible to determine, discover, or decide with certainty
2. too great, numerous, or complex to be measured or counted

Examples

• The exact cause of the disease remains indeterminable without further research.
• The age of the ancient artifact is indeterminable from visual inspection alone.
• The number of stars in the universe is indeterminable to the human mind.
• Her motives for leaving were indeterminable from her brief letter.
• The damage caused by climate change over centuries is indeterminable at this point.
• The true authorship of the manuscript is indeterminable after so many years.