Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
conclūsĭuncŭla, ae, f. dim. [conclusio, II. D.], a trifling or captious conclusion, a sophism: fallaces ( = σοφίσματα), Cic. Ac. 2, 24, 75: contortulae quaedam et minutulae conclusiunculae, id. Tusc. 2, 18, 42.