The suffix "-ish" means "a little bit" or "kind of". You put it on the end of an adjective, a noun, or a number. For example, if you're telling someone's age but you're not really sure if you have the number right, you say:
He's fiftyish, I'd say.
"-ish" is mostly used with adjectives that describe a quality that can have different amounts, like:
It doesn't sound as natural with adjectives that are "all or nothing", like "dead" or "finished". You can't be "a little" dead; you're either alive or you're completely dead. So it would be strange for someone to use the word "deadish" in a serious way.
You can also use "-ish" on the end of some nouns. There are only a few examples of this:
sluggish (This means "slow".)
However, the meaning of this is different from adjective + "-ish". The "-ish" ending on a noun makes it into an adjective. So "style" is a noun and "stylish" is an adjective. "Child" is a noun and "childish" is an adjective that means "acting like a child".