The phrase "tending to spread" implies that something is expanding or proliferating. Synonyms for this phrase include "contagious," "infectious," "diffusive," "propagating," "spreading," and "disseminating." "Contagious" suggests the transfer of a disease or emotion from one person to another. "Infectious" focuses more on the transmission of a disease. "Diffusive" indicates something spreading in an unfocused or scattered manner. "Propagating" and "spreading" highlight the idea of something expanding in a deliberate and intentional manner. Finally, "disseminating" emphasizes the act of sharing or spreading information or ideas to a wider audience.