Source : Webster's Revised Unabridged Dictionary (1913)

Monthly \Month"ly\, a.
   1. Continued a month, or a performed in a month; as, the
      monthly revolution of the moon.

   2. Done, happening, payable, published, etc., once a month,
      or every month; as, a monthly visit; monthly charges; a
      monthly installment; a monthly magazine.

   {Monthly nurse}, a nurse who serves for a month or some short
      time, esp. one which attends women after childbirth.

Monthly \Month"ly\, n.; pl. {Monthlies}.
   A publication which appears regularly once a month.

Monthly \Month"ly\, adv.
   1. Once a month; in every month; as, the moon changes
      monthly. --Shak.

   2. As if under the influence of the moon; in the manner of a
      lunatic. [Obs.] --Middleton.

Source : WordNet®

monthly
     adj : occurring or payable every month; "monthly payments"; "the
           monthly newsletter"
     n : a periodical that is published every month
     adv : without missing a month; "we get paid monthly" [syn: {every
           month}, {each month}]