hollow out

hollow out (third-person singular simple present hollows out, present participle hollowing out, simple past and past participle hollowed out)

1. (transitive) To make something hollow.
   • 1961 October, Voyageur, “The Cockermouth, Keswick & Penrith Railway”, in Trains Illustrated, page 601:

     After we have crossed the Glenderamackin stream, which drains the northern slopes of Saddleback, and the latter has united with the St. John's Beck to form the Greta, however, we see ahead the miniature canyon the Greta has hollowed out for itself, and into the depth of which the train now descends.

2. (intransitive) To become hollow.
3. (transitive) To reduce the power or influence of something.