Etymology
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footpad (n.)

"highwayman who robs on foot," 1680s, from foot (n.) + pad "pathway, footpath" (1670s), from Middle Dutch pad "way, path," from Proto-Germanic *patha- "way, path" (see pad (v.1), and compare path). Pad was a cant word among thieves and vagabonds, in expressions such as stand pad "stand by the wayside begging." Especially "one of a large class, existing in Europe when police authority was still in an ineffective condition, who made a business of robbing people passing on horseback or in carriages" [Century Dictionary]. 

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highwayman (n.)
"one who travels the highways with intent to rob people" (often on horseback and thus contrasted to a footpad), 1640s, from highway + man (n.).
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