Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Nī̆grīnus, i, m., Nī̆grīna, ae, f. [1. niger, swarthy], a Roman surname: C Pontius Nigrinus, Suet. Tib. 73.
Fem.: Nigrina, Mart. 4, 75; Inscr. Grut. 430, 3.