*reg- — de Vaan
*reg- 'to flow', as LIV does; but this does not change the problem of Latin -/-. Finally, it is conceivable that ir-rigare belongs to the root *rig- 'to stretch' reflected in rigeo. Semantically this is quite satisfactory; it would then be a fairly old (frequentative) derivative */«-ng-a- 'to lead into'. This etymology yields the most straightforward explanation of-/-· BibL: WH II: 435, EM 573f, IEW 857, Sihler … — [de Vaan, s.v. *reg-, p. 537]