Etymology: In senses 2 and 3, and perhaps also in sense 1 < Middle French rigole watercourse, gutter (1339; early 13th cent. in Old French in form regol in sense ‘part of a ditch where water flows’; French rigole ), of uncertain origin, perhaps < Middle Dutch rēgele , rēgel row, straight line, rule (see reghel n., rail n.²). Compare post-classical Latin rigolus channel, groove (1292, 1386 in British sources), Welsh rhigol groove, rut, furrow for planting, gutter (16th cent.; < English). The word was probably current in English in the senses ‘furrow’, ‘groove’, and perhaps also ‘gutter’ before the end of the 16th cent., and probably within the 15th cent.: see the evidence of rigol v. and of the variants riggle n. and (probably reflecting a variant of the same French word) regal n.²; compare also raggle n.² Sense 1 perhaps arose from application of the word to a groove running round something, although such intermediate uses are not found in English and neither these nor sense 1 itself are found in other languages. Association with ringle n.¹ is perhaps also possible (compare especially β. forms at ringle n.¹). Alternatively, sense 1 may show a different word: perhaps compare spec. uses of regal n.¹

Etymology: < rigol n. Compare Middle French, French rigoler to adjust (a water channel) in such a way that water flows freely (13th cent. in Old French; in modern regional use also ‘to cut drainage channels in’).