Any of the lines or streams in which light appears to radiate from a
luminous body. → light ray.
The straight line normal to the wave front in the propagation of radiant energy.
A stream of material particles all moving in the same straight line.
Etymology (EN): M.E. raie, raye, from O.Fr. rai “ray, spoke,” from
L. → radius “ray, spoke, staff, rod.”
Etymology (PE): Partow, ultimately from Proto-Iranian *pari-tap- “to shine around,
radiate away.”
The first component *pari- “around, about;” cf. Mod.Pers.
par-, pirâ- “around, about,” from
Mid.Pers. pêrâ; O.Pers. pariy “around, about,” Av. pairi
“around, over,” per- “to pass over, beyond;”
Skt. pari; Gk. peri “around, about,
beyond;” L. per “through;” PIE base *per- “through, across, beyond.”
The second component *tap- “to shine, radiate;” cf. Mod.Pers.
tâbidan, variants tâftan “to shine,” tafsidan
“to become hot;” Mid.Pers. tâftan
“to heat, burn, shine;” taftan “to become hot;” Parthian t’b “to shine;”
Av. tāp-, taf- “to warm up, heat,” tafsat “became hot,”
tāpaiieiti “to create warmth;”
cf. Skt. tap- “; to heat, be/become hot; to spoil, injure, damage; to suffer,”
tapati “burns;” L. tepere “to be warm,” tepidus “warm;”
PIE base *tep- “to be warm.”
