Vocabulary development significantly contributes to language proficiency, yet the journey of acquiring new words poses substantial challenges, particularly for English as a Second Language (ESL) learners. The objective of this study is to examine the particular difficulties encountered by ESL learners in acquiring new vocabulary and to gain insights into the root causes of these challenges. Additionally, the study seeks to explore effective targeted interventions that ESL teachers can employ to mitigate these difficulties. The study includes 520 9th-grade students (335 boys, 185 girls) from five rural secondary schools in Khurdha district, Odisha, India, during the 2023/2024 academic year, along with ten ESL teachers. To identify vocabulary learning difficulties, the researcher administered a vocabulary-learning difficulties questionnaire to students. Additionally, semi-structured interviews were conducted with teachers to understand the underlying reasons for these difficulties. Using SPSS version 28, the researcher analysed quantitative data, and thematic analysis was employed to analyse the qualitative date. The analysis revealed various difficulties in vocabulary learning, including difficulties in pronunciation, contextual usage, grammar comprehension, understanding homophones, homonyms, and homographs, spelling complex words, using collocates, phrasal words, and idioms, as well as memorization and translation issues. Interviews with teachers identified limited exposure to English, ineffective classroom instruction, lack of opportunities in vocabulary learning activities, and insufficient opportunities for reading and writing practice in English as primary reasons for vocabulary difficulties. The findings of the study offer valuable insights for ELT material developers, educational institutions, and language instructors, aiming to alleviate vocabulary learning challenges.