An Etymological Dictionary of Astronomy and Astrophysics

1. Physics: Any of the distinct patterns of oscillation that a given periodically varying system can have.
   

2. Math.: In a series of statistical data, the item or value which occurs most frequently. It is a measure of central tendency.

Etymology (EN): Mode, from Fr. mode, from L. modus “measure, rhythm, song, manner,” from PIE base *med- “to measure, limit, judge, advise;” cf. L. meditari “to think or reflect upon, consider;” Av. mad- “to measure out, apportion, allot;” Gk. medein “to rule;” O.E. metan “to measure out.”

Etymology (PE): Tarz “manner, mode,” Arabicized as طرز. Tarz may be related to Av. darəsa- “appearance, looking” (huuarə.darəsa- “having the appearance of the sun”), from Av. darəs- “to look;” cf. Skt. darś-, drś- “to see, appear, look, show” darśa- “apperance, look,” drśta- “apparent, visible.”
Mod, loan from Fr., cognate with Av. mad- “to measure out, apportion, allot,” as above.