1Used to say something is preferable or less bad compared with another option (often written マシ). It implies a choice isn't ideal but is still better than the alternative.
この古いパソコンでも動くなら、まだマシだ。
If this old PC still works, that's still better than nothing.
彼の意見は間違っているけど、何も言わないよりはマシだ。
His opinion is wrong, but it's better than saying nothing at all.
雨が降っているけど、傘があるからまだマシだ。
It's raining, but since I have an umbrella, it's still not so bad.
2As a noun or suffix (〜増し), it indicates an increase or extra amount (e.g. 100円増し, 'an extra 100 yen').
この席は窓側で、500円増しです。
This window seat costs an extra 500 yen.
革製のバッグは、同じモデルの布製より1000円増しだ。
The leather bag is 1,000 yen more than the cloth version of the same model.
3An archaic noun meaning increase or growth. Rarely used in modern Japanese.
古い文献には「産業の増し」という表現が見られる。
In old documents, one can find the expression 「産業の増し」 ('the growth of industry').