All known medieval and early modern Irish clans were named after men. There are no known examples of clans named after women. (Surnames) Whether a woman's descriptive adjective byname should be lenited depends on the last letter(s) in her given name and the first letter in the descriptive adjective byname. The default is that a woman's descriptive adjective byname should be lenited unless it starts with a vowel or the given name and byname meet the criteria indicated below. Gaelic bynames formed from the mother's or grandmother's name (metronymics) are vanishingly rare to nonexistent in both Scotland and Ireland. This style of Gaelic name & two generation patronymic byname is appropriate in both Gaelic Scotland and Ireland throughout the Middle Ages and Early Modern period.

 
A woman's descriptive adjective byname is always lenited unless
(Sorted by last letter(s) of given name:)(Sorted by first letter of descriptive adjective byname:)
The given name
ends with		AND the descriptive adjective byname
begins with		The given name
ends with		AND the descriptive adjective byname
begins with
-bB--b, -mB-
-cC-, G-(?)-c, -ch, -gC-
-chC-, G--d, -t(?), -th, -l, -n, -sD-
-dD-, T--fF-
-fF--c(?), -ch, -gG-
-gC-, G--l, -n, -r, -sL-
-lL-, N-, R-, D-, T--mM-
-mM-, B-, P--l, -n, -r, -sN-
-nL-, N-, R-, D-, T--m, -pP-
-pP--l, -n, -r, -sR-
-rL-, N-, R--sS-
-sS-, L-, N-, R-, D-, T--d, -t, -th, -l, -n, -sT-
-tD-(?), T-
-thD-, T-

Medieval Gaels each had a single given name chosen from a pool of names that depended on gender, specific time period, and specific Gaelic naming culture. In Gaelic Scotland and Ireland, when descriptive adjective bynames were used they were often combined with simple patronymic bynames. Descriptive bynames were sometimes used in both Gaelic Scotland and Ireland. These bynames were usually adjectives describing concrete rather than fanciful characteristics, such as beag (small), reamhar (stout), mór (big), ruadh (red), bán (fair), and dubh (black). Two generation patronymic bynames were sometimes used in both Gaelic Scotland and Ireland. These bynames are formed from the names of the individual's father and grandfather (father's father). Whether the father's given name should be lenited depends on period and dialect. In late period some Gaelic dialects (mainly in Scotland) would lenite the father's given name, but otherwise the father's given name was not lenited in men's simple patronymic bynames.

In Scotland, clan affiliations were not normally used in Gaelic bynames. You do not need to have any clan affiliation in mind to form a historically accurate Scottish Gaelic byname. Simple patronymic bynames and clan affiliation bynames are the two most common types of Gaelic byname found in medieval and early modern Ireland. In the 9th century the area that is now Scotland had almost half a dozen different cultures speaking as many different languages divided up into even more different kingdoms. In the southwest they were speaking Cumbric (a Brythonic language closely related to Welsh), in the southeast they were speaking Old English, in the northeast they were speaking Pictish, in the far north they were speaking Norse, and in the west they were speaking Gaelic. In Ireland, clan affiliations began to be used to form bynames from the 10th century and were often used to form bynames from about the 11th century. This basic style of Gaelic name & simple patronymic byname is appropriate in both Gaelic Scotland and Ireland throughout the Middle Ages and Early Modern period.

By the 12th century, Pictish and Cumbric had disappeared, but Norse, Gaelic, and English were still being spoken. The number of kingdoms had lessened, but the Kingdom of Scotland still did not have the borders of modern Scotland. Norway held the Northern Isles and most of the Western Isles, and the border with England was still being hammered out. Even in the 16th century, with her modern borders nearly set, there were still at least three languages spoken in Scotland; in addition to Doric and Scots, spoken primarily in the Lowlands, and Gaelic, spoken primarily in the Highlands and Western Isles, Norn as well as Scots was spoken in the Northern Isles.

Note that it is the father, and not the mother, whose given name is used to form the simple patronymic byname. Gaelic bynames formed from the mother's name are vanishingly rare to nonexistent in both Scotland and Ireland. In Ireland, clan affiliation bynames were often combined with simple patronymic bynames (again, common from about the 11th century, though possible from the 10th century). The names included in this guide from the Gaelic notes are those of people who lived in Scotland, primarily in the north east of Scotland, in the 11th and early 12th centuries. The names found in the Latin charter are included, but should be treated with caution, as some of them may not have been used by Gaels. The Latin names are not included in the analysis of the frequency of byname types. In other words, medieval Scottish names were very different from modern North American and European names.