Adjetivos em inglês terminados em Y

Ola pessoal,

Nem sei se este seria o titulo certo ja que nao tenho nem certeza se sao adjetivos, mas acho que sao. Procurei na lista de adjetivos aqui mas nao achei entao gostaria de saber mais sobre aquelas palavras que transformamos em adjetivos colocando o y no final por exemplo, greed, greey. smile, smiley. what are the rules to transform nouns to adjetives, also i'd like to know about informal english, other day i heard my husband describing a banana ice cream and he said "oh that ice cream is very banany" i don't even know if we would write like that and people say other words like that a lot, carroty, and he said they are not real words, is there a rule or list of adjectives is correct to say???

Thanks

Ps: Sorry guys I've just realised I started in portuguese the question and ended it in english lol