DeMundo 157:7 :ܘܡܡܛܪܢܐ ܘܡܫܡܗܝܢܢ ܠܗ݂܂ ܡܢ ܗܝ݁ ܕܡܡܛܪ ܘܐܝܬܘܗܝ ܒܐܬܝܪ‏ : we call it rainy since it produces rain and is in the air
See the entire entry for mamṭrān, mamṭrānā nom.ag.C one that rains