Although the suffix -issimo is one of the most common means of emphasis in Italian, adding a qualifier of "extremely" or remarkably," its use is not as simple as it might appear. In fact, the use of this suffix has a number of restrictions. For example, why don't the following terms exist in Italian: inascoltabilissimo, statalissimo, marittimissimo, egoistissimo, mancantissimo?
An overarching rule explaining all cases where the intensification of adjectives with -issimo is not permitted would be difficult and require a thorough analysis of the complex semantic structure of the adjectives. Instead, here is the general criterion: the suffix -issimo is only applicable for adjectives that can be preceded by the adverb molto.
Indeed, in Italian there is grandissimo (outsize), bellissimo (very beautiful), fortissimo (very loud, severe), and also molto grande, molto bello, molto forte. On the other hand, neither terms such as privissimo, agricolissimo, settimanalissimo, nor molto privo, molto agricolo, molto settimanale are acceptable in Italian. Reinforcing these last adjectives is obtained by different means, for example del tutto privo (completely devoid), proprio settimanale (every week).
However, there are many adjectives modified with molto and not with -issimo. This is the case of invariable adjectives (aggettivi invariabili). The color blu can lead to molto blu but not bluissimo; the term entusiasta can lead to molto entusiasta but not entusiastissimo.
Even compound adjectives (aggettivi composti) often do not allow the suffix -issimo; no native Italian would say fruttiferissimo or beneducatissimo (but ironically, the term maleducatissimo is acceptable).
Some limitations have probably arisen to avoid unpleasant or repeated sounds, such as those that would occur with redditizissimo, prolississimo, ottimisticissimo. Also, technical-scientific adjectives are generally not emphasized by adding -issimo: in medical language, for example, formations such as astigmaticissimo or vitaminicissimo are not found.
The general rule indicated, that adjective + -issimo is acceptable if molto + adjective is possible, does have exceptions, though. There are cases where the adjective can be intensified with -issimo but not with molto; think of phrases such as: "Sono fidanzati, anzi fidanzatissimi" (I'm engaged, rather I'm really, really engaged) or "Mi sento italianissimo" (I feel very Italian)." It is used in certain instances where -issimo is used to confirm a description: "fidanzatissimo" stands for "really and truly engaged."
Other examples include primissimo, ultimissimo, stessissimo, nessunissimo, vietatissimo, possibilissimo; all of which appear in modern Italian, as opposed to molto primo, molto ultimo, molto stesso, molto nessuno, molto vietato, and molto possibile, which do not.
Another aspect of the somewhat arbitrary use of the suffix -issimo is its application to certain nouns; in the language of sports there is il campionissimo, la partitissima; in advertising l'occasionissima, il mercatissimo; in correspondence gli augurissimi and i salutissimi (somewhat mawkish).
ITALIAN ADJECTIVES WITH SUPERLATIVE ENDING -ISSIMO
|abbondantissimo||very abundant, very copious|
|competentissimo||very expert, very qualified|
|fischiatissimo||very much booed, loudly booed|
|morbidissimo||very soft, very gentle, very smooth|
|notevolissimo||very notable, noteworthy or remarkable|
|quotatissimo||very often quoted|
|scollatissimo||very low-cut (neckline)|
|tifosissimo||very much a fan (of)|
|vaghissimo||very vague, very faint|