*gwere- gwera-, Proto-Indo-European root meaning "heavy." It forms all or part of: aggravate; aggravation; aggrieve; bar (n.4) "unit of pressure;" bariatric; baritone; barium; barometer; blitzkrieg; brig; brigade; brigand; brigantine; brio; brut; brute; charivari; gravamen; grave (adj.); gravid; gravimeter; gravitate; gravity; grief; grieve; kriegspiel; guru; hyperbaric; isobar; quern; sitzkrieg. It is the hypothetical source of/evidence for its existence is provided by: Sanskrit guruh "heavy, weighty, venerable;" Greek baros "weight," barys "heavy in weight," often with the notion of "strength, force;" Latin gravis, "heavy, ponderous, burdensome, loaded; pregnant;" Old English cweorn "quern;" Gothic kaurus "heavy;" Lettish gruts "heavy."

Sources:

• A Dictionary of Selected Synonyms in the Principal Indo-European Languages, University of Chicago (By: Carl Darling Buck) 1988.
• Etymological Dictionary of Latin and the other Italic Languages (By: Michiel de Vaan) 2008.
• The American Heritage Dictionary of Indo-European Roots (By: Calvert Watkins) 2000.
• Noun Declension in Indo-European (Sindhueuropaia Deklination Nomnes) By: Carlos Quiles.
• Online Etymology Dictionary (By: Douglas Harper)