knock against Copy link • knock against: offendo, di, sum, 3: to k. one's head against an archway, caput ad fornicem of., Quint. 6, 3, 67: to k. one's foot against something, of. pedem: v. to stumble. Phr.: to k. one's head against a stone wall (prov.), verberare lapidem, Pl. Curc. 1, 3, 41. See also to dash against, fall foul of.