Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sĭnistrorsus (collat. form sĭnis-trorsum, Hor. Epod. 9, 20; id. S. 2, 3, 50; and not contr. sĭnistrōversus, Lact. 3, 6, 4), adv. [contr. from sinistrovorsus, from sinister-vorto], towards the left side, to the left: hinc (Hercynia silva) se flectit sinistrorsus, Caes. B. G. 6, 25; Suet. Galb. 4; Front. Aquaed. 5: portu latent Puppes sinistrorsum citae, Hor. Epod. 9, 20: ille sinistrorsum, hic dextrorsum abit, id. S. 2, 3, 50: dextro aut sinistroversus, Lact. 3, 6, 4.