"Masteral" or "Master's"

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The moment you graduated a 4year course in college you may proceed to a higher education like going into a masters degree of your choice. One of my friend corrected us that there is no such term as Masterals. eg: what are you doing now? im in (masteral) degree now. as what he stress out. this is waht we should state it. Im in a master's degree now. Well for me, it sounds better and its in a correct grammar! what you think?