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

See also: periodical

• endoscope
• endoscopic
• endoscopy
• endoskeletal
• endoskeleton
• endosperm
• endospore
• endospore-forming bacteria
• endosteum
• endothelial
• endothelial myeloma
• endothelium
• endothermal
• endothermic
• endothermic reaction
• endotoxin
• endotracheal tube
• endovenous
• endow
• endowed
• endowment
• endowment fund
• endowment insurance
• endozoan
• endozoic