3 letters:
rak, rec, ric, roc

4 letters:
bike, dike, dyck, fike, fyke, hike, like, lyke, mike, pike, pyke, rack, rake, rech, reck, reek, reit, rice, rick, ride, riek, ries, rife, rile, rine, ripe, rise, rite, roch, rock, rook, ruck, ryer, ryka, ryle, tike, tyke, wike, wyke, zike, rike

5 letters:
heick, huyck, psych, reeck, reick, reihl, reiss, reisz, rhein, rhine, rhyme, rhyne, ricke, rieck, rieke, riesh, right, riker, rocke, rooke, roque, ruyle, ryker, teich, weich, wrack, wreak, wreck, wrice, write, wruck, reich

6 letters:
raisch, reicks, reisch, riecke, rocque, wright

7 letters:
reich's, reicher, reichow