RECTIFIABLE is a 11 letter word that starts with R.
\Rec"ti*fi`a*ble\ (r?k"t?*f?`?*b'l), a. 1. Capable of being rectified; as, a rectifiable mistake. 2. (Math.) Admitting, as a curve, of the construction of a straight l??e equal in length to any definite portion of the curve.