Korean has a deliciously diverse vocabulary with intricacies and nuances difficult for Korean Language Learners (KLL) to grasp. To gain true proficiency, KLL must learn to think like Koreans about the four types of Korean words: Native, Sino-Korean, mimetics, and loanwords. We hypothesize that native Korean speakers inherently understand differences between these categories of words, and we pose the questions: How do native Korean speakers understand the nuances, and how can that knowledge benefit KLL? Sino-Korean words are historically based on Chinese characters, each of which represents a root-word. Although a set of Sino-Korean words may be translated the same way in English, differences in the roots give the words different meanings in Korean. We investigate Sino-Korean word nuances by polling native Korean speakers on whether sets of synonyms are interchangeable. We also explore pairs of Native Korean and Sino-Korean words with similar meanings. Native speakers are surveyed on 22 pairs to see how they derive meaning from the Sino/Native distinction. Mimetic words are widely used and very expressive in Korean, describing not only sounds, but also depicting appearance, smells, movements, sensations, and psychological states. Mimetics have particular characteristics, such as meaningful consonant and vowel choices and rhythmic repetition of sounds, knowledge of which can help KLL understand how Koreans experience and express their sensations. Finally, loanwords are words from other languages that have been adopted into Korean. With technological advances and cross-cultural communication, such language influence is inevitable, and many Korean loanwords come from English. Increasingly, loanwords are combined with native words into compounds, contributing to a sharp rise in newly formed words (신조어) whose influence is spreading among Korean youth beyond social media. Understanding the four categories of Korean words can help a KLL understand the nuances and social significance of Korean vocabulary usage.