By Professor Brian ” Cuiv,
with the author's permission)
In Lexique …tymologique de l'Irandais Ancien
C-199, where the forms cossoit, cosait
are given as verbal noun of con-saidi,
we find as a derivative of this "cossaitech
'querreleur' ou 'qui se plainte' (d'ou NP O'Cassidy."
We may suppose that the compilers might postulate
Ua Cossaitig as a likely form of the surname
in the Middle Irish period. This is theoretically
possible since it would be on par with Ua Cleirig
from an ancestor Cleirech. The later
reflex of such a form would O Cosaoidigh
or, with a for o in the first
syllable as seen in the later v.n. casaoid,
” Casaoidigh. However, extant forms
of the surname do not, as far as I know, support
the statement in the Lexique.
The forms found in modern times are ” Caiside,
which would be a reflex of a Mid. Ir. Ua Caisite,
and ” Casaide. The form with palatalised
s is the one generally used by a number
of seventeenth-century O Caiside scribes and also
in other early sources, such as annals, but in some
instances the i-glide in the first syllable
was omitted to read Casside or Caside.
The Ui Chaiside were prominent from the fourteenth
century on in Fermanagh where many of them were
hereditary doctors to Mag Uidhir chieftans.
As is the case with many learned families their
origins are obscure. It seems likely that
the connection with Fermanagh went back to the twelfth
A late genealogical tract traces the family through
Cormac Cas, ancestor of Dal Cais, to Mil Easpainne
(Anal. Hib. 3. 136-7). The name Caiside
occurs at two points in the genealogy: eighth
and fifteenth down Cormac Cas. The earlier
Caiside is given as great-grandson of Caisin (which
probably for Caisin) "a quo an Fine."
The section showing the later one is as follows:
". . . mc Ghiollamachuada mhoir mc
Caiside, do bhi na ollamh leighis agus Seannchuis
is likely that the "Giollamachuada" of
the text is the Giolla Mo Dutu who composed the
metical banshenchas in 1147 and who is
described by Best and O'Brien in LL Vol.
III, p. viii, as "Gilla Mo Dutu ua Casaide."
According to his own account in the closing
stanzas of the poem he composed it in Daminis (
= Devinish on Lough Erne), but he had come from
Ard Brecain ( = Ardbreccan in Meath).
The name of the eponymous ancestor of the family
is quite unusual. It does not occur among
the personal names listed in Corp. Gen. Hib.
The comment "a quo an Fine" following
the name Caisin in the genealogy cited above and
the fact that the line goes back to Cormac Cas suggest
that the author of that genealogy saw a connection
between Caiside (earlier Caisite),
Caisin and Cas. Also uncommon
is the termination -ite, but it is seen
in the name Tipraite from which came the
surname ” Tiobraide (Tubridy). It
is noteworthy that in an early genealogy of the
Ui Chaisin(e) branch of the Dal Cais (Corp.
Gen. Hib. p. 248) a Tipraite appears five generations
down from Caisin.