1. In a thoughtless manner
   "he stared thoughtlessly at the picture"
   - unthinkingly, unthinking 
2. Showing thoughtlessness
   "he treated his parents thoughtlessly"

See also: thoughtless

Antonym: thoughtfully

• operationalist
• operationally
• operations
• operations research
• operative
• operative field
• operatively
• operator
• operator gene
• opercular
• operculate
• operculated
• operculum
• operetta
• operon
• operose
• operoseness
• Opheodrys
• Opheodrys aestivus
• Opheodrys vernalis
• Ophidia
• ophidian
• Ophidiidae
• ophidism
• Ophiodon