Here are some examples:
Hull
Husk
Hums
Hunt
Huts
Hurt
Hues
Hugs
Hubs
Noel (Christmas) is one holiday with four letters.
addseggsoddsAnnebeefbeenbeepbeerbeetbootbookboomboonbooscoolcootdeerdeepdeeddeemdoordoomfeedfeelfeetfoodfoolfootgoodgeedgoofgoongoopheedheelheedhoodhoofhoophootjeepjeerkeepkeelkeenleekleerloonloomlooplootmeetmoodmoonmoormootneednooknoonpeerpoofpeelpoolpeeppeerroofroomrootreedreelseedseemseenseerseessoonteentooltootwoolweedwoodwoofweep
Plum
Mesa
4 letter words, letters 2 and 3 are the same:allybeetbeenbeefbeepbeerbeesboomboonbootcookcoolcoopdeepdeeddeerdoomdoorfeedfeelfeesfeetfoodfoolfootgoodheelhoodhoofhoophootjeepkeepleerloomloonlooplootmeetmoodmoonseedeggsElla
Noel (Christmas) is one holiday with four letters.
Four letter words that begin with the letters cor- include:cordcorecorkcorn
addseggsoddsAnnebeefbeenbeepbeerbeetbootbookboomboonbooscoolcootdeerdeepdeeddeemdoordoomfeedfeelfeetfoodfoolfootgoodgeedgoofgoongoopheedheelheedhoodhoofhoophootjeepjeerkeepkeelkeenleekleerloonloomlooplootmeetmoodmoonmoormootneednooknoonpeerpoofpeelpoolpeeppeerroofroomrootreedreelseedseemseenseerseessoonteentooltootwoolweedwoodwoofweep
Plum
Mesa
shoe
jack, jazz
hymn
4 letter words, letters 2 and 3 are the same:allybeetbeenbeefbeepbeerbeesboomboonbootcookcoolcoopdeepdeeddeerdoomdoorfeedfeelfeesfeetfoodfoolfootgoodheelhoodhoofhoophootjeepkeepleerloomloonlooplootmeetmoodmoonseedeggsElla
Unna
Bold
A chef or cook have 4 letters and start with c.