From Longman Dictionary of Contemporary Englishovertaxo‧ver‧tax /ˌəʊvəˈtæks $ ˌoʊvər-/ verb [transitive] 1 WORK HARDto make someone do more than they are really able to do, so that they become very tiredovertax yourself Be careful you don’t overtax yourself.2 PETto make people pay too much tax→ See Verb table
Examples from the Corpus
overtax• Since the operation, he's been careful not to overtax himself.• His friend fears the difficult work may overtax his weak brain. 