Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† acro or acrōn, ōnis, m., = ἄκρων, the extremity of a thing; so of a member of the body, Veg. 2, 28, 17; 5, 65, 2; of the stem of a plant, Apic. 4, 4.