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§ 136 eryr benyw ‘female eagle’ the non-mutation of the b- of benyw shows that eryr remains mas. In fact the gender of a noun must be ascertained before gwryw or benyw can be added to it.

There are however several nouns of  gender in Welsh, that is, nouns whose gender varies according to the sex of the individual meant. Such are dyn ‘man’ or ‘woman’, dynan ‘little person’, cyfyrder ‘second cousin’, wyr ‘grandchild’, tyst ‘witness’ (< Lat. testis com.), mudan ‘deaf-mute’, perthynas ‘relation’, gefell ‘twin’, cymar ‘mate’, llatai ‘love-messenger’, etc. § 139 v, cyw ‘pullus’, llo ‘calf’. Thus y mudan or y fudan; y perthynas or y berthynas; llo gwryw or llo fenyw.

Some mas. nouns used as terms of endearment, etc. become fem. when applied to females; as peth ‘thing’, byd ‘life’, cariad ‘love’, enaid ‘soul’; thus y beth dlawd ‘poor thing’ f.
 * ’Y myd wen, mi yw dy ŵr,
 * A’th was i’th burlas barlwr.—D.G. 156.

‘My fair life, I am thy husband and thy servant in thy leafy parlour.’