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

See also: periodical

• icehouse
• Iceland
• Iceland lichen
• Iceland moss
• Iceland poppy
• Iceland spar
• Icelander
• Icelandic
• Icelandic krona
• Icelandic monetary unit
• Icelandic-speaking
• iceman
• icepick
• icetray
• ichneumon
• ichneumon fly
• Ichneumonidae
• ichnological
• ichnology
• ichor
• ichorous
• ichthus
• ichthyolatry
• ichthyologist
• ichthyology