English▸ adjective expressing opinions on matters outside the scope of one's knowledge or expertise:
“Dad, how do we know the universe is expanding?” inquires your six-year-old. Try answering that without resorting to an ultracrepidarian trick here or there.
▸ noun a person who expresses opinions on matters outside the scope of their knowledge or expertise:
most patients are ultracrepidarians when it comes to medicine.
– ORIGIN early 19th century : from Latin ultra ‘beyond’ and crepida ‘shoe, sandal’, with allusion to the remark ne supra crepidam sutor iudicaret ‘the cobbler should not judge beyond his shoe’, attributed to the painter Apelles of Kos in response to criticism from a shoemaker in Pliny the Elder's Natural History (ad 77).