strengthen, other, tithe, anthem, btrother, mother, father, enthral, pathway
authoranthemarithmeticanotherarrhythmicbreatherbrotherblatherbotherbathingbotherbathtubbreathingclothingcathetercathedralditherdeathwatcheitherethnicearthwormearthlyaetheretherfeatherfartherfathomfaithfulgatherGothicheatherhitherhealthyisthmuslatherlethalleatherloathingmothermythologymothballmarathonmethodmouthwashnorthernneitherotherpythonpathwaypantherratherruthlessrhythmsouthernsoothingtoothlesstithetruthfulwitherwithoutwithdrawwrathfulwithholdwitherwitheweatherwhetherwealthyzither
Some three letter words that have an A in the middle are:bagbahbanbarbatbaycabcadcamcancapcarcatcawcaydabdaddamdayeareatfadfanfarfatfaxgabgadgaggalgapgasgayhadhaghamhasHathayjabjamjarjawjaylabladlaglaplawlaymadmanmapmarmatmawmaynabnagnapnaypadpalpanparpatpawpayragrahramranrapratrawraysadsagsapsatsawsaxsaytabtadtagtamtantaptartattaxvanvatwadwagwanwarwaswaxwayyakyamyapyawzap
Some words that have the letter X in the middle are:asexualaxeboxerbuxomcoaxingcoexistDixieepoxiedfixedflexionhexedhoaxinglexismaximmixedmoxienexuspixelpixieproxiessexessixthsixtytaxedTexastoxictoxinvexedvixenwaxen
slothyouthfrothworthwrathclothbirthbrothsouthnorthgirthmouthmonthteethfifthsixthninthtruthwidthmirthfilthfaith
Some six letter words with FF in the middle are:wafflebafflebufferduffermufflepifflesufferduffelpuffindiffer
Words that have the letter I twice in the middle are skiing and coniine (it's a poison).
Some three letter words with a vowel in the middle are:airbowcatdogeatforguthitionjamkitlapmannotourpunquaratsiptapvatwinyewzoo
otherashesachesashenochreaphid
Some words with a letter P in the middle are:apeapplecapercoppercoprahelpfulmapleslipperspytaperuppervaporviperwiperzipper
words with ch in the middle:achearchesinchespitchersricherteachers
twelfth
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 1 words with the pattern TH---TH--. That is, nine letter words with 1st letter T and 2nd letter H and 6th letter T and 7th letter H. In alphabetical order, they are: thegither