1883, "rough grass or weeds, refuse of crops suitable for bedding for animals," from rough (adj.) + -age. In nutritional science, the meaning "coarse, bulky food" is attested by 1927.
Entries linking to roughage
rough adj.
Middle English rough (late 14c.), also rouhe, rouwe, roghe, rugh, etc., from Old English ruh, rug- "not smooth to the touch, coarse (of cloth); hairy, shaggy;" of hides, "undressed, untrimmed;" of ground, "uncultivated." This is from West Germanic *rukhwaz "shaggy, hairy, rough" (source also of Middle Dutch ruuch, Dutch ruig, Old High German ruher, German rauh), from Proto-Germanic *rukhaz, which is perhaps related to the source of Sanskrit ruksah "rough;" Latin ruere "to rush, fall violently, collapse," ruina "a collapse;" Lithuanian raukas "wrinkle," rukti "to shrink."
The original -gh- sound was guttural, as in Scottish loch. The form row was a regular variant from early 16c. and lingered in dialects. Of actions, "characterized by harshness or disparity," c. 1300; of land, terrain, late 15c. as "rugged, hard to traverse." Of stormy weather from mid-14c.; by late 14c. of turbulent seas, rude language, discordant sounds.
From mid-14c. as "crudely made;" c. 1600 as "rudely sufficient, not smooth or formed by art." Rough stone "undressed stone mortared together" is from mid-15c. Of writing or literary style, "lacking refinement, unpolished," 1530s. The sense of "approximate" is recorded from c. 1600.
Rough draft (or draught) is from 1690s. Rough-and-ready "rude and disorderly" is by 1832, from an earlier noun (1810), originally military; rough-and-tumble "not elaborately or carefully ordered" is from a style of free-fighting characterized by indiscriminate blows and falls (1810). Rough music "din produced by banging pots, pans, etc. for the purpose of annoying or punishing a neighbor" is by 1708. Rough-snout (c. 1300) was an old term for "a bearded face."
-age
word-forming element in nouns of act, process, function, condition, from Old French and French -age, from Late Latin -aticum "belonging to, related to," originally neuter adjectival suffix, from PIE *-at- (source of Latin -atus, past participle suffix of verbs of the first conjugation) + *-(i)ko-, secondary suffix forming adjectives (see -ic).