The Oxford Names Companion, OUP Clan MacLean Website and others
Notes:
Scottish Gaelic, Anglicized as Charles, from Old German "free man" or from Old English ceorl, "man". Tearlach is a modern shortened form of the Irish Gaelic Toirdhealbhach, possibly meaning "instigator".
Thanks to Donald Whyte who provided much of the initial information for this site.