• GROUPTHINK (noun). The noun GROUPTHINK has 1 sense: 1. decision making by a group (especially in a manner that discourages creativity or individual responsibility). Familiarity information: GROUPTHINK used as a noun is very rare. GROUPTHINK (noun). The noun GROUPTHINK has 1 sense: 1. decision making by a group (especially in a manner that discourages creativity or individual responsibility). Familiarity information: GROUPTHINK used as a noun is very rare.