semiannual (adj.)

• annual
• biannual
• biennial
• bimonthly
• biweekly
• catamenial
• centenary
• centennial
• daily
• diurnal
• fortnightly
• hebdomadal
• hourly
• menstrual
• momentary
• monthly
• quarterly
• quotidian
• secular
• semestral
• semimonthly
• semiweekly
• tertian
• triennial
• weekly
• yearly