conc▪ The meaning seems to have developed from the notion of *‘hollowness, cavity’ associated with the ‘navel’ (*‘cavity in the belly’). surur and the synonymous sirār therefore belong to the complex treated under ↗surr ‘umbilical cord’ and ↗surraẗ ‘navel’ and, as a whole, in the root entry ↗√SRː (SRR).
▪ But is perh. also surūr ‘joy’ (↗sarra) dependent on surur ‘line of the forehead, facial feature’, as *‘emotion recognizable from facial expression’?