Sentence:  The existing reverence for Centrality must have been still further <WSD>stimulated</WSD> toward the close of the second century B. C. , when the Han Emperor Wu Ti ordered the dynastic color changed to yellow - which symbolized the Center among the traditional Five Directions - and took 5 as the dynastic number , believing that he would thus place himself , his imperial family , and the nation under the most auspicious influences . 
Meaning of the word marked with <WSD> tags:  act as a stimulant