massed / mast are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
massed: (verb) join together into a mass or collect or form a mass.
mast: (noun) a vertical spar for supporting sails. (noun) nuts of forest trees (as beechnuts and acorns) accumulated on the ground. (noun) nuts of forest trees used as feed for swine. (noun) any sturdy upright pole.
massed: m·AE·s·t
mast: m·AE·s·t
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)