This quasi-experimental study investigated the effectiveness of Cognitive Linguistic-Based Instruction (CLBI) on the acquisition and long-term retention of intercultural political vocabulary among Vietnamese English as a Foreign Language (EFL) university students. Sixty participants were divided equally into an experimental group, receiving CLBI centered on Conceptual Metaphor Theory, and a control group ($n=30$), taught via traditional translation and rote-learning methods. Data collected through a pretest, an immediate posttest, and a four-week delayed posttest were analyzed using independent and paired samples t-tests. The results revealed that the experimental group achieved significantly higher scores in both posttests and demonstrated a remarkably lower vocabulary decay rate over time compared to the control group.