Carole Hough wrote:
>
> According to Reaney & Wilson, it's found as early as Domesday Book,
> in Herefordshire. They give: "OW _Seisill_, said to derive from Lat
> _Caecilius_".
>
> Hanks & Hodges: "Welsh: from the OW personal name _Seisyllt_,
> apparently a mutilated form of the L name _Sextilius_, a deriv. of
> _Sextus_ 'Sixth' ... The spelling has, however, been modified as a
> result of folk etymological association with the L name
> _C(a)ecilius_, a deriv. of _caecus_ blind."
>
> Morgan & Morgan, _Welsh Surnames_, has Cecil as a variant spelling of
> Seisyll, Seisyllt.

Many thanks - those are most interesting.  Although I find the etymologies 
somewhat dubious!  Would it be fair to say that Cecil is an anglicisation 
(in some sense...) of Seisyll, Seisyllt?  (Perhaps a latinisation for 
English consumption!)  I would also suggest an association with Cecilia.

John Briggs