presume Look up presume at Dictionary.com
late 14c., "to take upon oneself, to take liberty," also "to take for granted, presuppose," from O.Fr. presumer (12c.), from L. pręsumere (see presumption). Presumptive is recorded from 1560s. The heir presumptive (1620s) is "presumed" to be the heir if the heir apparent is unavailable.