The following nouns are always used in their singular forms, i.e. these nouns in German have no plural forms:
das Innere - inside
das Äußere – outside
das Gute – good
das Böse – evil
die Hetze - agitation
die Unsitte – bad habit
das All – universe
das Web – web
das Geld – money
die Gier – greed, lust
die Milch – milk
das Obst – fruit
die Politik - politics
die Diplomatie – diplomacy
die Solidarität – solidarity
das Lachen – laughter
das Marketing – marketing
das Wandern - hiking
das Wiegen - weighing
das Binden - bonding, tying
die Hingabe – devotion, dedication
das Vorkommen – incidence, occurrence
das Koffein – caffeine
das Leid – suffering, distress
das Elend – hardship, misery, distress