"a big square"
Well spotted! There are some nouns in Welsh which can be either masculine or feminine for various reasons of meaning (perhaps 15 or so), dialect (25-30, maybe more), usage (5-10?) or which can vary for no real reason at all. For example:
- y llif mawr - the big flood (m) (llifogydd - floods)
- y llif fawr - the big saw (f) (llifiau - saws)
- y de - the south (m)
- y dde - the right (f)
- Y Gymraeg, yr Almaeneg - the Welsh language, the German language (feminine nouns for names of languages)
- Cymraeg rhugl, Almaeneg da - fluent Welsh, good German (masculine nouns when describing an aspect of languages)
Sgwâr seems to be an example of the 'no real reason at all' group. Dewi Lingo seems undecided as to which gender of sgwâr to plump for at the moment, so with sgwâr he should accept bach/fach and mawr/fawr.