compound

definition: 
A thing that is composed of two or more separate elements; a mixture;A substance formed from two or more elements chemically united in fixed proportions
sentence: 
The air smelled like a compound of diesel and petrol fumes. The layers of plants and animals slowly broke down into simple substances called hydrocarbons, compounds of hydrogen and carbon.
difficulty: 
very easy
toefl frequency: 
2
toefl classification: