1) A curved piece of timber, one of a roughly matched pair, or two sawn from one tree.
Together they formed a rough arch, and two pairs at a distance supported the ridge timber of a building. In the OED the evidence for this term is late and appears under the headwords crock, crook and cruck. The Yorkshire examples are therefore important: 1352 ‘Margery del Milne is amerced 6d for felling trees … 40d for selling 6 crokkes’, Holmfirth
1380 ‘will build anew one grange of 6 posts or of six crokkes’, Yeadon
1454 ‘laying great stones under the foot of the Crokk’, Airton
1509 bield … a house of vj crokkys, South Crosland. Frequent references continue through the sixteenth century: 1573 to find great tymber and all other woode needful for the buildynge of one house of thre pare of crockes of whyte woode, Kilnsey.
2) An alternative spelling of ‘crouch’ in the sense of cross.