3 letters:
cid, cyd, cyr, dim, gym, him, jim, kim, kym, lim, mim, rim, sam, sib, sic, sid, sig, sil, sin, sip, sis, sit, som, sum, syd, syn, tim, vim, yim, zim, sim, sym

4 letters:
bihm, hymn, kimm, limb, mihm, pimm, pymm, saam, sahm, salm, same, saum, seam, sear, seem, seim, sejm, sere, shim, sick, siem, sigg, sill, sime, sims, sing, sinn, sipp, skim, slim, sohm, some, suhm, swim, syme, syms, timm, whim

5 letters:
sieve, simms, sims', singh, symms, timme

6 letters:
simmer, symmes