The term 'act as a proxy for' can be broken down into four crossword solutions: BEHALF (6 letters), INSTEAD (7 letters), ABSENTIA (8 letters), and COEN (4 letters). BEHALF is defined as on BEHALF of someone else, while INSTEAD is defined as in place of something else. ABSENTIA is defined as in the absence of someone or something, and COEN is defined as to act on BEHALF of another. Therefore, the term 'act as a proxy for' means to act on BEHALF of someone else in place of them, or in their absence.