“Matiner” means early riser. The Matiners’ War was started by a group of Carlists who rose in rebellion before the majority were ready.
Note: Spanish sources refer the the Matiner’s War as the Second Carlist War and to the 1872-76 affair as the Third Carlist War. Other, English, sources refer to the 1872-76 war as the Second Carlist War and the Matiner’s War as just that. I have followed the Spanish sources and adopted the first scheme.