An Etymological Dictionary of Astronomy and Astrophysics

To state that (something declared or believed to be true) is not true (Dictionary.com).

Etymology (EN): M.E. denien, from O.Fr. denoiir “deny, repudiate, withhold,” from L. denegare “to deny, reject, refuse,” from → de- “away” + negare “refuse, say no,”
from Old L. nec “not,” from PIE root *ne- “no, not.”

Etymology (PE): Niyârdan, literally “to bring (say) no,”
from ni-, variant of na→ not, → non-, → un-, + ârdan contraction of âvardan “to bring; to cause or produce,” → production.