3 letters:
pac, pad, pal, pam, pan, pap, pat

4 letters:
bath, fath, gath, hath, kath, lath, math, nath, pack, paff, pang, papp, pash, pass, patt, peth, pith, poth, puth, rath, vath, path

5 letters:
paeth, paque, patch, perth, plath, spath, wrath