rean
/riːn/noun
1A deep furrow used for conducting drainage water from a field or other piece of ground, a water-furrow; (also) a furrow between ridges in a ploughed field; = rain. Now English regional and Welsh English.
2A ridge, a baulk; a terraced strip; = rain. Now chiefly English regional.
Origin
Late Middle English; earliest use found in Palladius' De Re Rustica. Apparently ultimately related to rain, although the nature of the relationship is unclear. Perhaps a variant of that word (although the phonology poses difficulties: see below), or perhaps the reflex of an unattested Old English variant (with i-mutation) of Old English rān.