This research investigated the effect of contextual vocabulary teaching on high school students' levels of English language proficiency in Ethiopia. Although the national government has attempted to elevate the standards of English teaching, students end up finding it difficult to memorize and use vocabulary, which restricts their overall language ability. The purpose of this research is to establish whether vocabulary teaching in context, rather than decontextualized word lists, enhances secondary school students' language ability. A quasi-experimental design was utilized, with 60 students from two government high schools in Addis Ababa. The participants were allocated to control and experimental groups. The experimental group experienced contextual vocabulary instruction embedded within reading comprehension texts and classroom discussion, whereas the control group underwent traditional vocabulary drills. Pre- and post-tests were conducted to gauge vocabulary learning and language ability. The findings showed that students who were taught contextual vocabulary exhibited statistically significant vocabulary use, understanding, and language fluency improvement over the control group. The findings concur with constructivist learning principles, implying that meaningful usage of language enhances greater understanding. The research emphasizes instructional strategy impact on language acquisition outcomes and suggests curriculum reforms that prioritize context-based vocabulary instruction. Restrictions are short intervention duration and geographical specificity. In practice, the study suggests that in Ethiopia, teacher education and textbook development need to focus on context-embedded vocabulary activities. Socially, enhanced language ability can contribute to students' academic achievement and overall career potential in an age of globalization.