dewar / doer / dour / dur [du:r]
dewar – n. – a double-walled vessel with a vacuum between the walls to reduce the transfer of heat (i.e. a thermous)
doer – n. – 1. a person who does something; 2. one who acts rather than merely talking or thinking
dour – adj. – severe, stern or sullenly obstinate in manner or appearance
dur – adj. – musical term or major key (from German)