Etymology 1 
From Middle English rusch, risch, from Old English rysc, risc, from Proto-Germanic *ruskijō (compare West Frisian risk, Dutch rus (“bulrush”), dialectal Norwegian ryskje (“hair-grass”)), from Proto-Indo-European *resg- ‘to plait, wattle’ (compare Irish rusg (“bark”), Latin restis (“rope”), Latvian režģis ‘basketwork’, Albanian rrush (“grapes”), Serbo-Croatian rògoz, Ancient Greek ἄρριχος (arrikhos, “basket”), Persian رغزه (raɣza, “woollen cloth”)).
rush (plural rushes)
- Any of several stiff aquatic or marsh plants of the genus Juncus, having hollow or pithy stems and small flowers.
- The stem of such plants used in making baskets, mats, the seats of chairs, etc.
Etymology 2 
Perhaps from Middle English ruschen, russchen (“to rush, startle”), from Old English hryscan, hrȳscan (“to jolt, startle”), from Proto-Germanic *hruskijaną (“to startle, drive”), *hruskaną, *hurskaną (“to be quick, be clever”), from Proto-Indo-European *kors- (“to run, hurry”). Cognate with Old High German hurscan (“to speed, accelerate”), Old English horsc (“quick, quick-witted, clever”). More at hurry. Perhaps related to Albanian rash (“I fell, precipitate”).
An alternative etymology traces rush via Middle English rouschen (“to rush”) from Old English *rūscian from Proto-Germanic *rūskōną (“to rush, storm, be fierce, be cruel”), a variant (with formative k) of Proto-Germanic *rūsōną (“to be cruel, storm, rush”) from Proto-Indo-European *(o)rewǝ- (“to drive, move, agitate”), making it akin to Old High German rosc, rosci, Middle Low German rūschen, Middle High German rūschen, riuschen (German rauschen (“to rush”)), North Frisian ruse (“to rush”), Middle Dutch ruuscen (“to make haste”), Middle Dutch rūsen (Dutch ruisen (“to rush”)), Danish ruse (“to rush”), Swedish rusa (“to rush”). Compare Middle High German rūsch. Influenced by Middle English russhen (“to force back”) from Anglo-Norman russher, russer from Old French ruser, rëuser.
Alternatively, according to the OED, perhaps an adaptation of Anglo-Norman russher, russer (“to force back, down, out of place, by violent impact", "to pull out or drag off violently or hastily”), from Old French re(h)usser, ruser (although the connection of the forms with single -s- and double -ss- is dubious; also adopted in English ruse; French ruser (“to retreat, drive back”)), from an assumed Vulgar Latin *refusare and Latin refundere (“to cause to flow back”), although connection to the same Germanic root is also possible. More at rouse.
rush (plural rushes)
- A sudden forward motion.
- A surge.
- A rush of business can be difficult to handle effectively for its unexpected volume.
- General haste.
- Many errors were made in the rush to finish.
- A rapid, noisy flow.
- a rush of water
- a rush of footsteps
- (military) A sudden attack; an onslaught.
- (contact sports) The act of running at another player to block or disrupt play.
- a rush on the quarterback
- A sudden, brief exhilaration, for instance the pleasurable sensation produced by a stimulant.
- The rollercoaster gave me a rush.
- (US, figuratively) A regulated period of recruitment in fraternities and sororities.
- rush week
- (croquet) A roquet in which the object ball is sent to a particular location on the lawn.
Derived terms 
- (transitive or intransitive) To hurry; to perform a task with great haste.
- rush one's dinner
- (intransitive) To flow rapidly or noisily.
- (intransitive, soccer) To dribble rapidly.
- (transitive or intransitive, contact sports) To run directly at another player in order to block or disrupt play.
- (transitive) To cause to move or act with unusual haste.
- Don't rush your client or he may withdraw.
- (intransitive, military) To make a swift or sudden attack.
- (military) To swiftly attach to without warning.
- (transitive) To transport or carry quickly.
- The shuttle rushes passengers from the station to the airport.
- (transitive or intransitive, croquet) To roquet an object ball to a particular location on the lawn..
- (US, slang, dated) To recite (a lesson) or pass (an examination) without an error.
- See also Wikisaurus:rush (hurry)
Usage notes 
Used only before a noun.