"Dych chi eisiau petryal hir?"

Translation: Do you want a long rectangle?

[pablopublico]

Hir comes from Proto-Celtic *sīros ("long"), from Proto-Indo-European *seh₁-ro-, of which also descend Latin serus ("late"), which became French soir, Italian sera, Portuguese serão and Romanian seară, all meaning "evening".

[DaibhidhR]

It seems likely to me that it is also related to Gaelic searradh 'to stretch'. The meaning is fairly obviously related to 'long'. The other possible origin (Old Irish searr 'cut' does not seem likely to me) so this is the best etymology on the table.