What is the longest English word without a synonym?

Answer 1

ACETYL SERYL TYROSYL SERYL ISO LEUCYL THREONYL SERYL PROLYL SERYL­GLUTAMINYL PHENYL ALANYL VALYL PHENYL ALANYL LEUCYL SERYL SERYL VALYL­TRYPTOPHYL ALANYL ASPARTYL PROLYL ISOLEUCYL GLUTAMYL LEUCYL LEUCYL­ASPARAGINYL VALYL CYSTEINYL THREONYL SERYL SERYL LEUCYL GLYCYL­ASPARAGINYL GLUTAMINYL PHENYL ALANYL GLUTAMINYL THREONYL GLUTAMINYL­GLUTAMINYL ALANYL ARGINYL THREONYL THREONYL GLUTAMINYL VALYL­GLUTAMINYL GLUTAMINYL PHENYL ALANYL SERYL GLUTAMINYL VALYL TRYPTOPHYL­LYSYL PROLYL PHENYL ALANYL PROLYL GLUTAMINYL SERYL THREONYL VALYL­ARGINYL PHENYL ALANYL PROLYL GLYCYL ASPARTYL VALYL TYROSYL LYSYL VALYL­TYROSYL ARGINYL TYROSYL ASPARAGINYL ALANYL VALYL LEUCYL ASPARTYL­PROLYL LEUCYL ISOLEUCYL THREONYL ALANYL LEUCYL LEUCYL GLYCYL THREONYL­PHENYL ALANYL ASPARTYL THREONYL ARGINYL ASPARAGINYL ARGINYL ISOLEUCYL­ISOLEUCYL GLUTAMYL VALYL GLUTAMYL ASPARAGINYL GLUTAMINYL GLUTAMINYL­SERYL PROLYL THREONYL THREONYL ALANYL GLUTAMYL THREONYL LEUCYL­ASPARTYL ALANYL THREONYL ARGINYL ARGINYL VALYL ASPARTYL ASPARTYL­ALANYL THREONYL VALYL ALANYL ISOLEUCYL ARGINYL SERYL ALANYL ASPARAGINYL­ISOLEUCYL ASPARAGINYL LEUCYL VALYL ASPARAGINYL GLUTAMYL LEUCYL VALYL­ARGINYL GLYCYL THREONYL GLYCYL LEUCYL TYROSYL ASPARAGINYL GLUTAMINYL­ASPARAGINYL THREONYL PHENYL ALANYL GLUTAMYL SERYL METHIONYL SERYL­GLYCYL LEUCYL VALYL TRYPTOPHYL THREONYL SERYL ALANYL PROLYL ALANYL­SERINE = Tobacco Mosaic Virus, Dahlemense Strain.

This word has appeared in the American Chemical Society's Chemical Abstracts and is thus considered by some to be the longest real word.