An Etymological Dictionary of the German Language/langsam
ModHG. langsam, adj., ‘slow,’ is one of the earliest forms ending in sam (in Goth. only lustusams, ‘delightful, longed for’); AS. longsum, ‘tedious, continuous,’ OSax. langsam. In OHG., besides langsam, ‘lasting a long time,’ there exists a form langseimi, ‘lingering,’ and in MidHG. lancsam, adj. and adv., ‘slow,’ as well as lancseime, ‘lingering, slow’; in ModHG. langseim became obsolete, and its meaning has been transferred to langsam.