Merriam-Webster Inc. has added more than 100 entries to the latest edition of its Collegiate Dictionary. Here are some, along with the year in which Merriam-Webster researchers first found them used in an English-language publication, and their meanings: Acai (1868): a small dark purple fleshy berrylike fruit of a tall slender palm (Euterpe oleracea) of tropical Central and South America that is often used in beverages. Carbon footprint (1999): the negative impact that something has on the environment; specifically: the amount of carbon emitted by something during a given period. Cardioprotective (1984): serving to protect the heart. Flash mob (1987): a group of people summoned (as by e-mail or text message) to a designated location at a specified time to perform an indicated action before dispersing. Frenemy (1977): one who pretends to be a friend but is actually an enemy. Goji (2003): the dark red mildly tart berry of a thorny chiefly Asian shrub (Lycium barbarum) that is typically dried and used in beverages. Green-collar (1990): of, relating to, or involving actions for protecting the natural environment. Haram (1979): forbidden by Islamic law. Reggaeton (2003): popular music of Puerto Rican origin that combines rap with Caribbean rhythms. Shawarma (1953): a sandwich esp. of sliced lamb or chicken, vegetables, and often tahini wrapped in pita bread. Sock puppet (1959): a false online identity used for deceptive purposes. Staycation (2005): a vacation spent at home or nearby.