Place a superscript number after the closing period of the sentence you want to footnote.
Place a matching number at the bottom of the same page.
Use the following template to write your dictionary footnote after the number in APA style: "'Exogenous.' (2005). Merriam-Webster's Collegiate Dictionary. Springfield, MA: Merriam-Webster."
Use the following template to write your dictionary footnote after the number in Chicago style: "Merriam-Webster's Collegiate Dictionary, 11th ed., s.v. 'exogenous.'"
Use the following template to write your dictionary footnote after the number in MLA style: "'Exogenous.' Def. 2b. Merriam-Webster's Collegiate Dictionary. 2005. Print."