Why is the ninth month called September?
late 14c., from Old French dissimulation (12c.), from Latin dissimulationem (nominative dissimulatio) "a disguising, concealment," noun of action from past participle stem of dissimulare "make unlike, conceal, disguise," from dis- "completely" + simulare "pretend, assume, simulate" (see simulation).
dissimulation dis·sim·u·la·tion (dĭ-sĭm'yə-lā'shən)
Concealment of the truth about a situation, especially about a state of health, as by a malingerer.