[1650–60; ‹ L duotwo + -ad1]This word is first recorded in the period 1650–60. Other words that entered Englishat around the same time include: agency, burlesque, cardholder, oscillation, triplet-ad is a suffix occurring in loanwords from Greek denoting a group or unit comprisinga certain number, sometimes of years. Other words that use the affix -ad include: dyad, triad