reactive

1 ENTRIES FOUND:
reactive /riˈæktɪv/ adjective
reactive
/riˈæktɪv/
adjective
Britannica Dictionary definition of REACTIVE
1 
[more reactive; most reactive] : done in response to a problem or situation : reacting to problems when they occur instead of doing something to prevent them
— compare proactive
2 
chemistry : tending to change into something else when mixed with another substance