3 letters:
wok

4 letters:
bike, dike, fyke, hike, like, mike, pike, tike, tyke, wack, wake, walk, weak, week, weil, wick, wide, wife, wile, wine, wipe, wire, wise, woke, work

5 letters:
psych, reich, weiss, whack, while, whine, white, wight, wyden, wythe

7 letters:
weicker