Some longer than average words that start and end with the same letter are:
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redderarmadacosmicdemanddeniedgazinggapinggaminglethalrenterrockerstatustalentwillowyearly
Alliteration is when words that follow each other start with the same letter. E.G: crazy car, bouncy bunny...
alliteration
11 letter words that begin and end with the same letter:charismaticdisappeareddiscrediteddistributedgalvanizinggerminatingseriousnesstranslucenttransparent
Algebra, alfalfa, ammonia, amnesia and antenna are 7 letter words. They begin and end with the letter a.