graphdb/src/main/java/com/tinkerpop/blueprints/impls/orient/OrientBaseGraph.java
public <T extends Element> void dropKeyIndex(final String key, final Class<T> elementClass) {
    makeActive();

    if (elementClass == null)
      throw ExceptionFactory.classForElementCannotBeNull();

    executeOutsideTx(new OCallable<OClass, OrientBaseGraph>() {
      @Override
      public OClass call(final OrientBaseGraph g) {
        final String className = getClassName(elementClass);
        getRawGraph().getMetadata().getIndexManager().dropIndex(className + "." + key);
        return null;
      }
    }, "drop key index '", elementClass.getSimpleName(), ".", key, "'");

  }
public <T extends Element> void dropKeyIndex(final String key, final Class<T> elementClass) {
    makeActive();

    if (elementClass == null)
      throw ExceptionFactory.classForElementCannotBeNull();

    executeOutsideTx(new OCallable<OClass, OrientBaseGraph>() {
      @Override
      public OClass call(final OrientBaseGraph g) {
        final String className = getClassName(elementClass);
        getRawGraph().getMetadata().getIndexManager().dropIndex(className + "." + key);
        return null;
      }
    }, "drop key index '", elementClass.getSimpleName(), ".", key, "'");

  }
Drops the index against a field name.

@param key          Field name
@param elementClass Element class as instances of Vertex and Edge