concrete in WordNet English dictionary

1. a strong hard building material composed of sand and gravel and cement and water
   concrete 
   

1. form into a solid mass; coalesce
   concrete 
   
2. cover with cement
   "concrete the walls"
   concrete 
   

1. capable of being perceived by the senses; not abstract or imaginary
   "concrete objects such as trees"
   concrete 
   
2. formed by the coalescence of particles
   concrete