The word „nice“ can be used as a shortcut, either with or without the „s“. I have seen that it is most often used without, but it seems that both are accepted. (But NB, the short form would never match in terms of gender.) If words that usually belong to another part of the language are used as adjectives, they are immutable: non-adjectives. If you choose not to agree on these adjectives, you will agree with most dictionaries, so it will be difficult for a prescriptive reader or Mrs. Thistlebottom, the teacher/examiner, to decide that you have misunderstood. On the other hand, this choice isn`t really based on actual usage data – it`s just an arbitrary preference at the end of the day. As in general for adjectives that, for one reason or another, do not look like normal French words (either language words or shortened forms as in this case), dictionaries at least tend to think that they are immutable – in other words, you never add a match. You would write „sexy men“, „nice people“, etc. In French, most adjectives come according to the noun. Familiarize yourself with the constitution of sentences that contain adjectives and how you can „reconcile“ them with the nouns that describe them. There are also immutable adjectives that don`t fit into any of the above categories: Some adjectives like nice and bio are abbreviated forms of longer words and the only concordance they take is a plural -s. For example: to make the feminine, would you add an „e“ as a normal adjective? or a „him“ as in blanche? or replace the „c“ with a „that“ as in public? or add a „that“ as in Greek? None of these options seem to be correct. However, to some extent, this is a hypothesis or invention on the part of dictionary writers and prescriptive grammars that are not based on actual data.

As Clare says, if you look at the actual usage, you`ll see that – at least in fairly informal ways of writing – people sometimes add the „s“. Thus, people sometimes wrote „sexy men“, „nice people“, etc. 2. The adjective is an abbreviated form of a longer adjective, and the ending is cut off with the second half of the word. Most immutable adjectives fit into one of the following groups: Concordance for adjectives depends on the true number: Some adjectives follow different rules for how they correspond to nouns…