to be involved from the beginning in something that is likely to be very successful
The rewards can be great when you are in on the ground floor of an economic recovery.
Thesaurus: to take part, or to become involvedsynonym
Main entry: ground floor
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informal become part of an enterprise in its early stages
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be/get in on the ground ˈfloor idiom
to become involved in a plan, project, etc. at the beginning
Useful english dictionary. 2012.