No, the word "preplan" does not require a hyphen. It is a compound word that combines "pre" and "plan" without any punctuation between them.
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 1 words with the pattern --EP-A-. That is, seven letter words with 3rd letter E and 4th letter P and 6th letter A. In alphabetical order, they are: preplan
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 1 words with the pattern --EPL--. That is, seven letter words with 3rd letter E and 4th letter P and 5th letter L. In alphabetical order, they are: preplan
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 3 words with the pattern --EP--N. That is, seven letter words with 3rd letter E and 4th letter P and 7th letter N. In alphabetical order, they are: erepsin preplan stepson
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 2 words with the pattern P-E--AN. That is, seven letter words with 1st letter P and 3rd letter E and 6th letter A and 7th letter N. In alphabetical order, they are: plebean preplan
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 4 words with the pattern PR---AN. That is, seven letter words with 1st letter P and 2nd letter R and 6th letter A and 7th letter N. In alphabetical order, they are: preplan pridian propman protean
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 1 words with the pattern P-EPL--. That is, seven letter words with 1st letter P and 3rd letter E and 4th letter P and 5th letter L. In alphabetical order, they are: preplan
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 6 words with the pattern --E-L-N. That is, seven letter words with 3rd letter E and 5th letter L and 7th letter N. In alphabetical order, they are: avellan gremlin kremlin moellon preplan theelin
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 12 words with the pattern ---P-AN. That is, seven letter words with 4th letter P and 6th letter A and 7th letter N. In alphabetical order, they are: chapman gripman misplan outplan pampean preplan propman salpian shipman shopman triptan utopian
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 8 words with the pattern -R--L-N. That is, seven letter words with 2nd letter R and 5th letter L and 7th letter N. In alphabetical order, they are: drumlin ermelin graplin gremlin kremlin ortolan prawlin preplan
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 11 words with the pattern -R--LA-. That is, seven letter words with 2nd letter R and 5th letter L and 6th letter A. In alphabetical order, they are: areolae areolar areolas argalas arollas gravlax graylag greylag ortolan preplan triclad
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 3 words with the pattern PR-P--N. That is, seven letter words with 1st letter P and 2nd letter R and 4th letter P and 7th letter N. In alphabetical order, they are: preplan propman propmen