'astylar' originates from New Latin/Modern Latin, ultimately built from Greek elements: the privative prefix 'a-' meaning 'without' and 'stylos' meaning 'column' or 'pillar'.

'astylar' entered English via New Latin/Modern Latin (e.g. 'astylaris') and usage in architectural descriptions; the formation comes directly from Greek roots rather than from an Old English source.

Initially it meant 'without columns' in technical architectural contexts, and this specific meaning has been preserved into modern usage.