Carn Fiaclach
Carn Fiaclach, a 749m Simm near Loch Rannoch 

A Simm is a hill in Britain that is at least 600 metres high and has a drop of at least 30 metres on all sides. The name Simm is derived from Six-hundred Metre Monteto, where monteto is the word for hill in Esperanto. The second M may therefore stand for mountain, mam, meall, mullach, moel or mynydd according to the nature and location of the hill. The Simms have a simple definition but a complex history. They were introduced by Alan Dawson in 2010 as a way of unifying several of his own published lists that he had come to regard as unnecessarily complicated and outdated:

Most of these booklets are now out of print, though copies of the last two are still available and include useful notes about numerous hills. The Simms have not as yet been published as single unified list. More information about the Simms is available in these sources:

By the end of 2015 just two people had climbed all the Simms, Ken Whyte and Iain Thow.

Subsimms are British hills that are at least 600 metres high and have a drop of 20-29.9m drop on all sides. By the end of 2015 around 660 of them had been identified and listed.