Kays 229:19 :ܐܝ݂ܬܝܗ݀ ܥܠ݂ܬܗܝܢ ܕܡܬ݂ܟܢܫܝܢ ܣ݁ܓܝ݂ ܒܬܚ̈ܬܝܬܗ݀ ܕܐܪܥܐ ܒܥܘ݂ܒ̈ܐ ܥܡܝ݂ܩ̈ܐ‏ : their cause is that they collect in large amounts in the nethermost parts of the earth in deep caverns
See the entire entry for taḥtāyā, taḥtāytā n.f. lower part