To have sexual intercourse with (someone) for the first time, thereby depriving them of virginity. He boasted that he had deflowered her during the summer holiday.
To take away the beauty, freshness, or innocence of something. The construction of the new highway deflowered the once pristine landscape.
(archaic) To remove the flowers from (a plant, area, etc.); to strip of blossoms. The children deflowered the garden, leaving the shrubs bare.