Type.
A kind of fungus.
Hare
Fish
It depends on what you mean by 'four letter word'. Thea has four letters, so yes it is. It is not a swear word, so it's not that kind of 'four letter word'.
kiss kick kind knit
ilk
kind, eked, oaks, tank
There is only one particular kind of rectangle and that is a square - where all four sides are of the same length.
flounder
cod
kill, kind, kiss, Kris
Kind, kill, keep, kink, kook