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

See also: periodical

• coalescing
• coalface
• coalfield
• coalfish
• coalhole
• cask
• casket
• caskful
• Casmerodius
• Casmerodius albus
• Caspar
• Caspar Bartholin
• caspase
• caspase-mediated cell death
• Casper
• Caspian
• Caspian Sea
• casque
• casquet
• casquetel
• Cass Gilbert
• Cassandra
• cassareep
• cassation
• cassava