Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
percussūra, ae, f. [percutio], a blow, stroke, thrust (post-class.): percussura ferro facta, App. Herb. 31; Veg. Vet. 2, 20, 1; Vulg. Lev. 14. 54.