1.roost v.栖息(to perch)

例：A sparrow roosted in the small tree.

2.rotate v.旋转(to revolve)；轮作(to cause to grow in rotation)
词根记忆：rot(旋转)+ate(使…)--旋转
例：A circular rim is rotating 300 times per second.//rotate the crops轮种庄稼

派生词：rotation(n．旋转)

3.rotational a．转动的；轮流的(of or pertaining to rotation)
词根记忆：来自rotation(n．旋转，回转)
例：Outside the nucleus the rotational velocity would decrease geometrically with distance from the center.

同根词：rotatable(a．可旋转的；可循环的)

4.roughly ad.大概(approximately)；粗暴地(in a rough manner)
词根记忆：来自rough(a．粗暴的)

例：Total dollar sales for each of the company's divisions have remained roughly constant.

5.round v.四舍五入(to express as a round number);完成(to bring to completion);a.圆的(circular);n．圆(circle)

例：When the decimal is rounded to the nearest hundredth, 3.24 is the result.

6.royalty n．皇室（royal status or power）；版税，专利税(a payment to an author or composer for each copy of a work sold or to an inventor for each item sold under a patent)
词根记忆：来自royal(a．皇室的)
例：Faculty members should retain the royalties from books and articles they write.

同根词：royalist(n.保皇主义者；a．保皇的)

7.rudder n.船舵( broad flat piece of wood or metal hinged vertically at the stern of a boat or ship, used for steering)

例：Mary turned the rudder sharply to avoid hitting the rock.

8.rudimentary a．基础的，初步的（fundamental）；发育不全的(very imperfectly developed)
词根记忆：rudi(无知的，粗鲁的)+ment+ary--无知状态--初步的
例：Technology for tabulating census information was rudimentary during the first half of the 19th century.

同根词：erudite(a．深奥的)

9.rug n.（小）地毯(floor-mat)；毛毯(a piece of thick heavy fabric used as a blanket or covering)
例：The floor is covered by a rug.