under
In addition to the idioms beginning with under, also see below (under) par; born under a lucky star; buckle under; come under; cut the ground from under; don't let the grass grow under one's feet; everything but the kitchen sink (under the sun); fall under; false colors, sail under; get under someone's skin; go under; hide one's light under a bushel; hot under the collar; keep under one's hat; knock the bottom out (props out from under); knuckle under; light a fire under; nothing new under the sun; of (under) age; out from under; plow under; pull the rug out from under; put the skids under; six feet under; snow under; sweep under the rug; water over the dam (under the bridge).