"pro tem." YourDictionary, n.d. Web. 17 August 2018. <http://www.yourdictionary.com/pro-tem>.
pro tem. (n.d.). Retrieved August 17th, 2018, from http://www.yourdictionary.com/pro-tem
From the Latin phrase; pro tempore. The preposition pro means "for" and tempore is the ablative of tempus meaning "time".