r

R, 18th letter of the alphabet, corresponding to Greek rho. When in Latin alphabets the letters for p and r became similar in appearance, the rho form (P; which at first was used for the r sound) was restricted to the p sound, and an extra line was added for the r sound (R). In Greek, where no confusion developed, the rho continued to look like Latin P. A modification of R is the symbol ℞, used medically for recipe [Lat.,=take] and liturgically for responsum [Lat.,=response].

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r

(nucleonics)

roentgen

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R

(nucleonics)

roentgen

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R

1. Abbr. for “radius.”

2. Abbr. for “right.”

3. Symbol for the capacity of a pile (for example, 3R indicates three times design capacity).

4. Symbol for the thermal resistance of a material or component of construction.

5. Symbol for electrical resistance.

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sound reduction index, R

British term for sound transmission loss.