Racket-tailed (a.)
definition: Having long and spatulate
Or racket-shaped tail feathers.
Racket-tailed is a 13 letter word that begins with an R and ends in a D

Radiciflorous (a.)
definition: Rhizanthous.

Radiciflorous is a 13 letter word that begins with an R and ends in an S

Radius vector
definition: A straight line (or the length of such line) connecting any point
As of a curve with a fixed point or pole round which the straight line turns and to which it serves to refer the successive points of a curve in a system of polar coordinates. See Coordinate n.
Radius vector is a 13 letter word that begins with an R and ends in an R

Radius vector (n.)
definition: An ideal straight line joining the center of an attracting body with that of a body describing an orbit around it
As a line joining the sun and a planet or comet or a planet and its satellite.
Radius vector is a 13 letter word that begins with an R and ends in an R

Ragman's roll
definition: The rolls of deeds on parchment in which the Scottish nobility and gentry subscribed allegiance to Edward I. of England
A. D. 1296.
Ragman's roll is a 13 letter word that begins with an R and ends in an L

Ramollescence (n.)
definition: A softening or mollifying.

Ramollescence is a 13 letter word that begins with an R and ends in an E

Randall grass
definition: The meadow fescue (Festuca elatior). See under Grass.

Randall grass is a 13 letter word that begins with an R and ends in an S

Ratiocination (n.)
definition: The process of reasoning
Or deducing conclusions from premises; deductive reasoning.
Ratiocination is a 13 letter word that begins with an R and ends in an N

Ratiocinative (a.)
definition: Characterized by
Or addicted to ratiocination; consisting in the comparison of propositions or facts and the deduction of inferences from the comparison; argumentative; as a ratiocinative process.
Ratiocinative is a 13 letter word that begins with an R and ends in an E

Ratiocinatory (a.)
definition: Ratiocinative.

Ratiocinatory is a 13 letter word that begins with an R and ends in a Y

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