Beyond what could be imagined; unimaginable. Often used with of: undreamed luxuries; a peaceful settlement undreamed of a generation ago. (adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "undreamed" in a sentence
"The oil explorers began to fan out over the globe, finding it in undreamed of quantities."
"Not only have we found that the arable belt is very much larger than had been thought -- but that the forests and rocks contain undreamed of wealth."
"Although, as I said before, I know only a few insects, I at once had the impression of something undreamed-of, something extremely bizarre — the impression, let us say, of an insect from the moon."