If you mean the three same letters in a row, well, current English does not allow words like bulllike or frillless and prefers to hyphenate them: bull-like, frill-less.
But other languages can allow these formations. In German, there is Schifffahrt (water transportation) and in Estonian there is 'jaaaar' (actually with tremas on the a's), which means edge of the ice.
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Raccoon is a word. It includes double letters in a row.
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'What' is a four letter word, 'for' a three letter word, 'which' has five letters, 'yet' is spelled with three while 'it' has only two.