"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].
1610s, "unconcerned" (the sense that now would go with uninterested), from dis- "opposite of" + interested. The sense of "impartial" originally was in disinteressed (c. 1600), from Old French desinteresse, and subsequently passed to uninterested. The modern sense of disinterested, "impartial, free from self-interest or personal bias, acting from unselfish motives," is attested by 1650s.
By late 18c. the words had sorted themselves out, and as things now stand, disinterested means "impartial," uninterested means "caring nothing for the matter in question," and disinteressed has fallen by the wayside. Related: Disinterestedly; disinterestedness.
Disinterested and uninterested are sometimes confounded in speech, though rarely in writing. A disinterested person takes part in or concerns himself about the affairs of others without regard to self interest, or to any personal benefit to be gained by his action; an uninterested one takes no interest in or is indifferent to the matter under consideration .... [Century Dictionary]
Old English scip "ship, boat," from Proto-Germanic *skipa- (source also of Old Norse, Old Saxon, Old Frisian, Gothic skip, Danish skib, Swedish skepp, Middle Dutch scip, Dutch schip, Old High German skif, German Schiff), "Germanic noun of obscure origin" [Watkins]. Others suggest perhaps originally "tree cut out or hollowed out," and derive it from PIE root *skei- "to cut, split" (see schizo-).
Now a vessel of considerable size, adapted to navigation; the Old English word was used for small craft as well, and definitions changed over time; in 19c., distinct from a boat in having a bowsprit and three masts, each with a lower, top, and topgallant mast. French esquif, Italian schifo are Germanic loan-words.
Phrase ships that pass in the night is from Longfellow's poem "Elizabeth" in "Tales of a Wayside Inn" (1863). Figurative use of nautical runs a tight ship (i.e., one that does not leak) is attested from 1965.