pleh₂k-
“to strike, beat”Source of Latin plangere, English plague, plangent, plaint
Root for striking, yielding Latin plangere (to beat the breast in grief) and English plague, complain.
Discussion
The PIE root *pleh₂k- (to strike, to beat, to hit with a flat surface) produced the vocabulary of striking, lamenting, and affliction — connecting the physical blow to the emotional and medical consequences of being struck.
Latin plangere (to strike, to beat the breast in grief — the gesture of mourning is a self-inflicted blow) gave English: plangent (resounding with a mournful sound — the ringing of a struck bell or a beating chest), complain (com-plangere, to strike together — to beat the breast in shared grief, hence to express dissatisfaction), and plaintiff (the one who strikes/beats in grief — the one who brings a legal complaint).
Latin plāga (a blow, a wound, a stripe — from *pleh₂g-) gave English: plague (a blow from the gods — disease conceived as divine punishment) and the derived plaguey/plaguesome.
Greek plḗssein (πλήσσειν, "to strike") gave: apoplexy (apo-plēxía, "a striking away" — a sudden paralytic stroke), and the combining form -plegia (paraplegia, hemiplegia — partial striking/paralysis).
The root connects to *bʰreg- (to break) and *gʷenh₂- (to strike/kill) as part of the PIE vocabulary of violent impact. Where *bʰreg- emphasised breaking and *gʷenh₂- emphasised killing, *pleh₂k- emphasised the flat-handed blow — the slap, the beating, the percussive impact that rings.