Which adjective describes a situation that is dangerously lacking in security or stability?

The adjective that best describes a situation that is dangerously lacking in security or stability is "precarious." This term conveys a sense of instability and insecurity, suggesting that the situation is not only risky but also precariously tenuous and vulnerable to failure or danger. In contexts where safety is a concern, "precarious" implies that conditions are insufficient or unreliable, leaving room for potential collapse or harm.

While "unsafe" and "risky" might also suggest danger, they do not specifically connote a lack of stability in the same way that "precarious" does. "Secure," on the other hand, directly contradicts the idea of instability or insecurity and therefore does not fit the context of the question. Thus, "precarious" clearly captures the danger and fragility of a situation that is lacking in security or stability.