plum: (noun) a fruit; the tree that grows the fruit; (adjective) ideal; highly desirable; a reddish-purple colour
plumb: (adjective) to be perfectly vertical; to be perpendicular to the base; (noun) a weight, traditionally lead, on a piece of string (commonly referred to as a plumb bob); (verb) to measure the depth of a body of water; to test or adjust the verticality of a structure; to connect to a plumbing system; to work as a plumber