I. adjective
Date: 1926
: indicating a quantity whose algebraically positive and negative values serve to bracket a range of values either alone or when added to and subtracted from a given number
measured with an accuracy of plus or minus 3 feet
a mummy aged 3500 plus or minus 150 years
II. adverb
Date: 1849
: more or less , approximately
a dance for singles plus or minus age 30