Webster's English Dictionary

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rust

1. rust \'r*st\ n [ME, fr. OE ru-st; akin to OE re-ad red - more at RED] 
   1a: the reddish brittle coating formed on iron esp. when chemically attacke 
   d by moist air and composed essentially of hydrated ferric oxide 1b: the 
   similar coating produced on any of various other metals by corrosio n 1c: 
   something resembling rust : ACCRETION  2: corrosive or injurious influence 
   or effect  3: any of numerous destructive diseases of plants produced by 
   fungi (order  Uredinales) and characterized by reddish brown pustular 
   lesions; also : a fungus causing this 4: a strong brown 
2. rust vi 1: to form rust : become oxidized {iron ~s}  2: to degenerate 
   esp. from inaction, lack of use, or passage of time {mo st men would ... 
   have allowed their faculties to ~ -T.B.Macaulay} 3: to become reddish brown 
   as if with rust {the leaves slowly ~ ed} 4: to be affected with a rust 
   fungus  1: to cause (a metal) to form rust {keep up your bright swords, for 
   the  dew will ~ them -Shak.} 2: to impair or corrode by or as if by time, 
   inactivity, or deleterious us e 3: to cause to become reddish brown : turn 
   the color of rust