1. Having no justifying cause or reason
   "a senseless, causeless murder"; "a causeless war that never had an aim"
   - reasonless 
2. Having no cause or apparent cause
   "a causeless miracle"
   - fortuitous, uncaused

See also: unintended, unmotivated

• cycad family
• Cycadaceae
• Cycadales
• Cycadofilicales
• Cycadophyta
• Cycadophytina
• Cycadopsida
• Cycas
• Cycas circinalis
• Cycas revoluta
• Cyclades
• Cycladic civilisation
• Cycladic civilization
• Cycladic culture
• cyclamate
• cyclamen
• Cyclamen hederifolium
• Cyclamen neopolitanum
• Cyclamen purpurascens
• cycle
• cycle of rebirth
• cycle on
• cycle path
• cycle per second
• cycle rickshaw