Which term means to prevent or obstruct by taking action ahead of time?

The term that means to prevent or obstruct by taking action ahead of time is "forestall." This word suggests a proactive approach where actions are taken in advance to ensure that something undesirable does not occur. For instance, law enforcement might take preventive measures to address potential criminal behavior before it happens, which illustrates the concept of forestalling.

In contrast, the other terms focus on different aspects of interference. "Delay" refers to causing something to happen later than planned, rather than preventing it altogether. "Impede" suggests hindering progress or movement, but not necessarily through preemptive action. "Stall" implies causing a stop or pause in progress, which doesn't directly convey the idea of preemptive obstruction. Thus, forestall is the most precise term for taking anticipatory action to prevent an event from occurring.