foot (n.) Look up foot at Dictionary.com
"terminal part of the leg of a vertebrate animal," Old English fot "foot," from Proto-Germanic *fot (cognates: Old Frisian fot, Old Saxon fot, Old Norse fotr, Danish fod, Swedish fot, Dutch voet, Old High German fuoz, German Fuß, Gothic fotus "foot"), from PIE *ped- (1) "a foot" (cognates: Avestan pad-; Sanskrit pad-, accusative padam "foot;" Greek pos, Attic pous, genitive podos; Latin pes, genitive pedis "foot;" Lithuanian padas "sole," peda "footstep"). Plural form feet is an instance of i-mutation.

In Middle English also "a person" (c.1200), hence non-foot "nobody." Meaning "bottom or lowest part of anything eminent or upright" is from c.1200. Of a bed, grave, etc., from c.1300. On foot "by walking" is from c.1300. The linear measure was in Old English (the exact length has varied over time), this being considered the length of a man's foot; a unit of measure used widely and anciently. In this sense the plural is often foot. The medieval Paul's Foot (late 14c.) was a measuring standard cut into the base of a column at the old St. Paul's cathedral in London. The metrical foot (late Old English, translating Latin pes, Greek pous in the same sense) is commonly taken to represent one rise and one fall of a foot: keeping time according to some, dancing according to others.

To get off on the right foot is from 1905 (the wrong foot is by 1949); to put one's best foot foremost first recorded 1849 (Shakespeare has the better foot before, 1596); Middle English had evil-foot (adv.) "through mischance, unluckily." To put one's foot in (one's) mouth "say something stupid" is attested by 1942; the expression put (one's) foot in something "make a mess of it" is from 1823. To have one foot in the grave "be near death" is from 1844. Colloquial exclamation my foot! expressing "contemptuous contradiction" [OED] is attested by 1923, probably euphemistic for my ass in the same sense, which dates to 1796 (also see eyewash).
foot (v.) Look up foot at Dictionary.com
c.1400, "to dance," also "to move or travel on foot," from foot (n.). From mid-15c. as "make a footing or foundation." To foot a bill "pay the entirety of" is attested from 1848, from the process of tallying the expenses and writing the figure at the bottom ("foot") of the sheet; foot (v.) as "add up and set the sum at the foot of" is from late 15c. (compare footnote (n.)). The Old English verb gefotian meant "to hasten up." Related: Footed; footing.