íssimos

íssimos is a Portuguese superlative suffix. It is added to adjectives to indicate an extreme degree of the quality described by the adjective. For example, "bonito" (beautiful) becomes "boníssimo" (extremely beautiful). This suffix is used to emphasize the intensity of the adjective. It is a common and widely used grammatical feature in Portuguese.

The formation of the superlative with -íssimo generally involves taking the adjective, removing its final vowel (if it has one), and adding the suffix. For masculine singular adjectives, it is -íssimo. For feminine singular, it is -íssima. For masculine plural, it is -íssimos, and for feminine plural, it is -íssimas. For instance, "feliz" (happy) becomes "felicíssimo" (extremely happy), "felicíssima" (extremely happy, feminine), "felicíssimos" (extremely happy, masculine plural), and "felicíssimas" (extremely happy, feminine plural).

This superlative form is used in both spoken and written Portuguese to add expressiveness and emphasis. It is a more formal and literary way to express a high degree of a quality compared to using adverbs like "muito" (very) or "extremamente" (extremely), although those adverbs are also common. The use of -íssimo can convey a stronger, more vibrant sense of the adjective's meaning.