a transparent (virtually literal) idiom

an opaque binomial

a literal trinomial

an opaque idiom

a figurative idiom whose meaning can be surmised

a semi-opaque trinomial

now you are a small fish in a big pond rather than a big fish in a small pond

they are as different as chalk and cheese

she waited till he kicked the bucket

he ummed and ahed

mad, bad and dangerous to know

blood, sweat and tears