the twelfth month of the year, containing 31 days. Abbreviation:Dec.
Origin: bef. 1000; ME decembre < OF < L december (s. decembr-) the tenth month of the early Roman year, appar. < *dec(em)-membri-, equiv. to decemten+ *-membri- < mens- month + -ri- suffix (with -sr- > -br- and assimilation of nasal)
De·cem·ber (dĭ-sěm'bər) n.
Abbr. Dec. The 12th month of the year in the Gregorian calendar. See Table at calendar.
[Middle English decembre, from Old French, from Latin December, the tenth month of the Roman year, probably from *decemmembris, from *decem-mēnsris : decem, ten; see dek in Indo-European roots + mēnsis, month; see menses.]
de·cre·scen·do (dā'krə-shěn'dō, dē'-) adv.
& adj. Abbr. dec. With gradually diminishing force or loudness. Used chiefly as a direction. n.
pl.de·cre·scen·dos
A gradual decrease in force or loudness.
A decrescendo passage.
[Italian, gerund of decrescere, to decrease, from Latin dēcrēscere; see decrease.]
[di-sem-ber] 
in Indo-European roots + mēnsis, month; see menses.]