Languages › Spanish Units of Time in Spanish 'Unidades de tiempo' Share Flipboard Email Print Reloj solar en Zaragoza, España. (Sundial in Zaragoza, Spain.). Photo by Juandc.com; licensed via Creative Commons. Spanish Vocabulary History & Culture Pronunciation Writing Skills Grammar By Gerald Erichsen Spanish Language Expert B.A., Seattle Pacific University Gerald Erichsen is a Spanish language expert who has created Spanish lessons for ThoughtCo since 1998. our editorial process Gerald Erichsen Updated May 12, 2017 Need to know how to refer to a particular unit of time? Here are the most common ones in Spanish, listed from the shortest period of time to the longest: el nanosegundo — nanosecond el microsegundo — microsecond el milisegundo — millisecond el segundo — second el minuto — minute la hora — hour el día — day la semana, el septenario — week la quincena — fortnight, two weeks (The term sometimes refers to a 15-day period or a half-month.) el mes — month el semestre — six months, half-year (The term can also refer to an academic semester.) el año — year el lustro — five years el decenio, la década — 10 years, decade el siglo — century el milenio — millennium el cron — million years el eón — thousand million years, billion years in U.S. English (The term also can refer to an indefinitely long period of time.) In addition, Spanish has a number of units of time that are seldom used, or are used in specific contexts. For example, bimestre and trimestre, are two-month and three-month periods, respectively, with similar month groupings possible. Similarly, bienio and septenio are two- and seven-year periods of time, respectively, with other groupings possible.