doctrinaire (n.)

1820, from French doctrinaire "impractical person," originally "adherent of doctrines" (14c.), from Latin doctrina (see doctrine).

At first used in the context of French politics, contemptuously applied by rival factions to those who tried to reconcile liberty with royal authority after 1815. Hence, anyone who applies doctrine without making allowance for practical considerations (1831). As an adjective, from 1834.