Quiz: Remember the definition of mal de mer?
1590s, "acting as if benumbed," alteration of Middle English clumsid "numb with cold" (14c.), past participle of clumsen "to benumb, stiffen or paralyze with cold or fear," from a Scandinavian source akin to Old Norse klumsa "make speechless, palsy; prevent from speaking," intensive of kluma "to make motionless." For insertion of -s-, cf. flimsy.
Not in general use until 18c., with senses "manifesting awkwardness; so made as to be unwieldy." Related: Clumsily; clumsiness. Cf. Swedish dialectal klummsen "benumbed with cold," Norwegian klumsad (past participle) "speechless, palsied by a spasm or by fear or witchery;" German verklammen "grow stiff or numb with cold." Also cf. clumse (n.) "a stupid fellow."