Learn Portuguese (Portugal): Que pena! Ela bebeu apenas meia taça de vinho. - What a pity! She drank only half a goblet of wine.

In this sentence, the word acts as an adjective meaning "half of a", so it must agree with the feminine singular noun it modifies (taça). If it were acting as an adverb meaning "kind of" or "a bit" (for example, if she were a bit tired), it would stay as the invariable meio.

In English we say "half a goblet". Why isn't it meia uma taça?

Portuguese does not use the indefinite article (um or uma) after meio or meia when saying "half a [noun]". You simply place the adjective directly before the noun, making it meia taça.

Why use taça instead of copo for a glass of wine?

While you will often hear people ask for um copo de vinho in casual conversation, a taça specifically refers to a stemmed glass or goblet, which is the traditional glassware for wine or champagne. A copo usually refers to a standard, stemless glass used for water or juice.

In the phrase Que pena!, why isn't there a word for "a" like in the English "What a pity"?

When using Que to make an exclamation (meaning "What a...!"), Portuguese does not use an article. You just link Que directly to the noun or adjective. Literally, pena means sorrow or pity, making Que pena! the standard way to say "What a pity!" or "What a shame!"