Partial reduplication of שָׁחוּם.
שְׁחַמְחַם • (sh'khamkhám) (feminine שְׁחַמְחַמָּה, masculine plural שְׁחַמְחַמִּים, feminine plural שְׁחַמְחַמּוֹת) [pattern: קְטַלְטַל]