IshGen 25:6 :ܐܫܬܛܚܬ ܘܗܘ݂ܬ ܐܝܟ ܡܕܡ ܫܕܬܐ‏ : it flattened and became like some kind of base
See the entire entry for šiddā, šiddəṯā n.f. base, chest