An Etymological Dictionary of Astronomy and Astrophysics

1. A feeling of uncertainty about the truth, reality, or nature of something. → skepticism.
   

   2. To be uncertain about; consider questionable or unlikely; hesitate to believe (Dictionary.com).

Etymology (EN): M.E. douten, from O.Fr. douter “doubt, be doubtful,” from L. dubitare “to doubt, question, hesitate” (related to dubius “uncertain”), from duo, “→ two,”

• habere “have, hold,” with a sense of “of having two minds, undecided between two things;” cf. Pers. dodeli, as below.

Etymology (PE): Gomân, from Mid.Pers. gumân “doubt;” ultimately from Proto-Ir. *ui-man-, from suffixed *man- “to think,” → idea.
Šakk, loan from Ar.
Dodeli, literally “having two minds,” from do, → two, + del, → heart (also meaning “soul, spirit, will, desire, courage, mind”); cf. Sogdian δβanā (from *dwa-nā), Ger. Zweifel, and L. dubius, as above.