There are two theories about the origin of the suburb's name. One is that the name comes from a hill where a pennant was flown as a signal during the early days of New South Wales. However, though such signals were certainly used, there is no evidence that such a pennant was ever flown at what is now Pennant Hills, but in the early 19th century the name applied to the whole ridge down as far as Mobbs Hill, which has a Telegraph Road to commemorate the signalling station. Also, references to the suburb of Pennant Hills were written 20 years before the establishment of pennant stations (Patrick 1994:79–80). Elizabeth MacArthur records receiving a flag signal at Parramatta that her husband John had returned from England in 1806. The other theory says that Pennant Hills was named after an 18th-century botanist, Thomas Pennant (Patrick 1994:79–80), though there is no contemporary evidence for this either. The fact that the area was first referred to as "Pendant Hills" in the Sydney Gazette when first published in 1803 makes this theory unlikely, as there was no Thomas Pendant either.