synclinal (adj.) Look up synclinal at Dictionary.com
"sloping downward on both sides," 1833 (in Lyell), from -al (1) + Latinized form of stem of Greek synklinein "to incline, lean," from syn- "together" (see syn-) + klinein "to slope," from PIE root *klei- "to lean" (see lean (v.)).