Purpose: Vocabulary acquisition is a critical component of second language (L2) learning, influenced by linguistic, cognitive, and contextual factors. Despite extensive research on vocabulary acquisition, there remains a gap in understanding how word frequency, familiarity, and morphological knowledge interact within different linguistic contexts. Previous studies have often examined these factors separately, but this study aims to bridge this gap by investigating their combined effects. This study examines the interplay of word frequency, word familiarity, and morphological knowledge in English vocabulary acquisition among ESOL learners at Bristol City College.

Methodology: A quantitative, cross-sectional design was employed, involving 184 ESOL learners enrolled at a language center in Bristol. Data were collected using a structured questionnaire and vocabulary tests, analyzed via variance-based Structural Equation Modeling (SEM) using SmartPLS (Version 4.0).

Findings: The results indicate that word frequency, word familiarity, and morphological knowledge significantly influence vocabulary acquisition. Morphological knowledge emerged as the strongest predictor, followed by word familiarity and word frequency. Notably, the effect of morphological knowledge varied across first language (L1) groups, demonstrating a greater impact for Arabic and European language speakers than for learners from other linguistic backgrounds.

Significance: These findings underscore the need for vocabulary instruction that integrates morphological training, strategic exposure to high-frequency and familiar words, and consideration of learners’ linguistic backgrounds. The study contributes to theoretical models of second language acquisition (SLA) and provides practical insights for ESOL pedagogy, advocating for tailored instructional strategies that address the cognitive and linguistic challenges of multilingual learners.