rare Designating spiral mollusc shells that coil to the left (anticlockwise), and molluscs having such shells; = "sinistral".
Of a plant or plant part: twining or turning to the left (anticlockwise).
The apparent direction of twining depends upon whether the viewer is taken to be standing within or facing the spiral, leading to the use of the word in opposite senses.
3 rare That moves or goes towards the left.
Mid 19th century; earliest use found in William Macgillivray (1796–1852), ornithologist and natural historian. From post-classical Latin sinistrorsus, adjective from classical Latin sinistrorsus (also sinistrorsum) (adverb) to the left, contracted from *sinistrōvorsus, from sinistr-, sinister left + -ō, suffix forming adverbs + vorsus, variant of versus.