Real Dictionary

steal someone's thunder in British English
to appropriate or use another's idea, plan, words, etc.
to detract from the attention due to another by forestalling him or her
to stop someone from getting attention or praise by doing something better than them or doing something before them
to use for one's own purposes and without the knowledge or permission of the originator the inventions or ideas of another
to use someone's ideas or methods without permission and without giving credit