[small piece, fragment] late 14c., scrappe, "piece of food remaining after a meal" (usually plural), from Old Norse skrap "scraps; trifles," from skrapa "to scrape, scratch, cut" (see scrape (v.)).
Hence, "any remnant or small, detached piece" (1580s), typically negative (not a scrap) or in reference to something written or printed. The dismissive term scrap of paper is attested by 1840, made infamous in 1914 by the German chancellor's comment when violating the treaty that guaranteed Belgian neutrality.
The meaning "remains of metal produced or collected after rolling or casting to be reworked" is from 1790. Scrap-iron is attested by 1794.
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy).