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Webster 1913 Edition

Noun.

A low hill at the foot of higher hills or mountains.

foothill ‎(plural foothills)

A hill at the base of a mountain or mountain range.
- 2012, July 15. Richard Williams in Guardian Unlimited, Tour de France 2012: Carpet tacks cannot force Bradley Wiggins off track
  The summit of the climb came 38km from the end of stage 14, which began in Limoux and ended in Foix in the foothills of the Pyrenees, and the incident occurred as the peloton emerged into the light and passed under the banner at the top, a quarter of an hour behind a five-man breakaway.

hill at the base of a mountain