Source : Webster's Revised Unabridged Dictionary (1913)

Semimonthly \Sem`i*month"ly\a.
   Coming or made twice in a month; as, semimonthly magazine; a
   semimonthly payment. -- n. Something done or made every half
   month; esp., a semimonthly periodical. -- adv. In a
   semimonthly manner; at intervals of half a month.

Source : WordNet®

semimonthly
     adj : occurring twice a month; "a semimonthly publication" [syn: {bimonthly}]
     adv : twice a month; "salaries are paid semimonthly" [syn: {bimonthly}]