1) In place-names, for dense tree growth.
The many meanings of ‘thick’ which are on record from the Old English period include ‘dense’, used of trees or woods. The word could be a noun in its own right, and in 1579 a Craven document listed a certain Thycke or Ryse of Thornes and Underwood in Littondale. As an adjective it is commonly found in minor place-names, linked with different types of trees: 1277 Thyckeholyns
that is hollies
1300 Thykthorndale
that is thorns
1421 Thykwethyns
that is willows and 1472 Thekehesils
that is hazels. It was rarely used of the ash or oak but one example has been recorded: 1681 a close or parcel of ground called Thickoakes, Selby. Examples of the word occur in letter books for the Dartmouth estate, kept now in the estate office in Slaithwaite, and they include its use as a verb: 1806 Thicken Campinot Plantation and Meal Hill Wood
1807 found Owlers Wood growing quite thick from the Larch which I had planted three years since. It can be contrasted with ‘light’ above.