deviationist n : an ideological defector from the party line (especially from orthodox communism)
In Stalinist Communism a deviationism is an expressed belief which is not in accordance with official party doctrine for the time and area.
A deviationist is person who expresses a deviation. The Ffestiniog Railway found another use for the word "Deviationists", for the gang of voluntary enthusiasts who formed the construction gangs to build its deviation. (Following British railway terminology, a deviation is a new route between two points taken as a result of the original route becoming unusable, for whatever reason. A much earlier 19th century example was in the Borough of Crewe where the Crewe to Chester line was subject to a deviation.)
Since the Ffestiniog, several heritage railways have found themselves in similar situations, and have had to muster great volunteer efforts to overcome physical and geographical difficulties.