Januar

By thys fyre I warme my handys

Februar

And with my spade I delfe my landys

Marche

Here I sette my thinge to sprynge

Aprile

And here I here the fowlis synge

Maij

I am as lyght as byrde in bowe

Junij

And I wede my corne well i-know

Julij

With my sythe my mede I mawe

Auguste

And here I shere my corne full lowe

September

With my flayll I erne my brede

October

And here I sawe my whete so rede

November

At Martynesmasse I kylle my swyne

December

And at Christes masse I drynke redde wyne*

So I found the above poem describing the yearly farming cycle. And in the second last stanza, beneath November, it says 'At Martynesmasse I kylle my swyne." So what on Earth is Martynesmasse?