mestrenco = mustangMUSTANG, the wild or semi-wild horse of the prairies of America, the descendant of the horses imported by the Spanish after the conquest in the 16th century ( see Horse ). The word seems to be due to two words in Spanish, mestrenco or vagabond, defined by Minsheu ( 41 1599; as " a strayer. " Mestrenco ( now Mesteno ) means " wild, having no master, " and it seems to be derived from mesta, a livestock Association, which took over all the wild cattle herds are among other functions.