Antonyms for "am deficient in" could include "proficient in," "skilled in," "adept at," "capable of," or "competent in." These words suggest an ability to perform well or excel in a particular area, which is the opposite of being deficient or lacking. Other possible antonyms could include "abundant in," "plentiful in," or "awash in," which imply an abundance or surplus of something rather than a shortage or deficiency. No matter the antonym used, the opposite of being deficient in something implies a level of proficiency, expertise, or abundance that can be beneficial in many situations, whether personal or professional.