If you dream up a plan or idea, you work it out or create it in your mind.
I dreamed up a plan to solve both problems at once...我想出了一个方案，可以同时解决两个问题。The event was dreamed up by Mick Jagger...这事是米克·贾格尔的凭空捏造。
想起, 想象出(不寻常的事物); 凭空设想
In his spare time, he always dreams up new stories.在业余时间, 他经常编新故事。He would never dream up a desperate scheme like that on his own.他绝不会想出那样一个不顾一切的计划。The plot of the film is simply dreamed up.这个电影的情节完全是虚构的。
1. devise or invent;
"He thought up a plan to get rich quickly""no-one had ever thought of such a clever piece of software"