It depends which dictionary you use, but roughly 44:
airn, akin, alif, anil, aril, fail, fain, fair, farl, fiar, fila, fink, firn, flak, flan, flir, ilka, kaif, kail, kain, karn, kiln, kina, kirn, knar, lain, lair, lank, lari, lark, liar, link, linn, lira, naif, nail, nark, rail, rain, raki, rani, rank, rial, rink.
Five letter words that can be made with the letters in 'Thanksgiving' are:agingangstankhsgainsgaitsgangsgiantgnashgnatshangshankshintskingsknishknitsnightninthsaintsatinshanksightstainstankstingstinktanksthankthingthinkthinsvisitvista
Words that can be made from the letter is 'with' are:hihitIitwit
Words that can be made with the letters 'aer' are:aareearera
Four letter words that can be made from the letters in 'Olympics' are:clipclopcloycoilcopylimplispmoiloilyployposysiloslimslipslopsoil
Five letter words that can be made from the letters in 'knighthood' are:dingodoingingotnightthighthingthinkthong
Four letter words that can be made from the letters in 'twinkle' are:kilnkiltkiteknewknitlentlienlikelinelinklintnewttiletinetwinweltwentwilewiltwinewink
beefsbeefybeetsbesetbestsbytescystsfecesmeetsmessymetessectsseemsstemsstyesteemsyeseszebeczestszestyzymes
Three letter words:aidanddindipdunnapnippadpanpinpun
Words that can be made from the letter in meal are:aalealmamlamlamemaleme
Five letter words that can be made from the letters 'one hundred' are:droneendedendererodeheronhonedhordehoundroundudderunder
Three letter words that can be made with the letters 'bingo' are:bigbinboggingobionnibobi
The two letter words that can be made from the word 'cooperate' are:atorpato