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Webster 1828 Edition

pp.

Made better, wiser or more excellent; advanced immoral worth, knowledge or manners.

Made better; advanced in fertility or other good qualities.

Used to profit or good purpose; as opportunities of learning improved.

Used; occupied; as improved land.

improved ‎(comparative more improved or further improved, superlative most improved or furthest improved)

That has been made better; enhanced.
- 2012, Meerbaum, ‎Richard S. Meltzer, Myocardial Contrast Two-dimensional Echocardiography
  The second is to develop a new generation of further improved contrast agent that can yield more intense myocardial contrast after intravenous injection.

that has been made better

improved