1. In a sporadic manner
   - sporadically 
2. At regular time intervals

See also: periodical

• reduction division
• reduction gear
• reductionism
• reductionist
• reductive
• reductivism
• redundance
• redundancy
• redundancy check
• redundant
• redundantly
• reduplicate
• reduplication
• reduplicative
• reduviid
• Reduviidae
• redux
• redwing
• redwood
• redwood family
• Redwood National Park
• redwood penstemon
• reebok
• reecho
• reechoing