The term 'be proficient in' can be described by four crossword solutions: ADEPT (5 letters), ABLE (4 letters), VERSED (6 letters), and excelat (7 letters). ADEPT means to have a natural or acquired skill, while ABLE implies having the power or capacity to do something. VERSED means to have knowledge or experience in a particular subject, and excelat suggests to be very good at something. All of these words imply that someone is proficient in a certain area.