3 letters:
cap, cop, cup, kip, kol

4 letters:
cape, capp, coad, coal, coan, coat, cobe, code, coey, cohn, coke, cole, comb, cone, coop, copa, copp, cose, cote, cove, cupp, dope, hope, kapp, kaup, keep, kepp, kipp, koen, kohl, koke, kole, kolk, kolm, kolp, koop, kopp, kote, lope, mope, nope, pope, rope, soap, sope, tope, cope, koep, kope

5 letters:
co-op, coach, coale, cocke, colle, combe, coped, copes, coppa, coupe, kaupp, knope, koehl, koehn, kohne, koper, kopke, koppe, kothe, scope, shope, koepp

6 letters:
koehne, koelle, koepke

7 letters:
schoepe, schoepf, schoepp