My sister and I would appreciate your comments on our web site. www.jimannelinthicum.com/.
In addition to a family genealogy, stories and photos, the site has a link to a UK site that describes a community named Lyncombe in Somerset which is south of Wales. The original Thomas Linthicum could have been an "English Gentleman" (not a Welshman) from Lyncombe which is near Wales.
If the origin of the name is a location then Thomas may not have been the only Linthicum to come to the colonies (although the spelling my be unique to Thomas).