DeMundo 136:26 :ܠܐܘܣܝܐ ܕܝܢ ܕܫܡܝܐ ܘܕܟܘܟ̈ܒܐ݂܂ ܩܪܝܢܢ ܠܗ݂݀ ܐܬܝܪ‏ : we term the substance of the heavens and the stars "aether"
See the entire entry for ˀūsīyā n.f. essence, being