Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
irrĕcūsābĭlis (inr-), e, adj. [2. inrecusabilis], not to be refused (post class.): occasio, Cod. Just. 3, 1, 13; Hier. Ep. 60, 14.
Hence, adv.: irrĕcūsābĭlĭter, without possibility of refusal, Rustic. c. Aceph. p. 1218.