|Ne forte offéndas ad lápidem pedem tuum.||Lest perhaps you should strike your foot against a stone.|
This is the second half of the previous clause, which is why offendas is in the subjunctive.
forte = perhaps (adverb). By chance, perchance.
ad lapidem = to the stone, against the stone.
pedem tuum = your foot, from pes, pedis, foot. Many English words have their root in the Latin word for foot: pedestal, podiatry, pedal, pedestrian.