Holtrop rhymes with:
gilstrap, kladstrup, westrup, autoeurope, balthrop, bearup, borup, europe, gawthrop, gilstrap, harrop, kladstrup, lathrop, lothrop, moulthrop, northrop, northrup, thorup, waldrep, waldrip, waldrup, westrup, winthrop
Holtrop sounds like:
heliotrope, hoelterhoff, holderby, holdorf, holtorf