motive Look up motive at Dictionary.com
mid-14c., "something brought forward," from O.Fr. motif (n.), from motif (fem. motive), adj., "moving," from M.L. motivus "moving, impelling," from L. motus, pp. of movere "to move" (see move). Meaning "that which inwardly moves a person to behave a certain way" is from early 15c.