  Dynamics of average length of words in Russian and English is analysed in the
article. Words belonging to the diachronic text corpus Google Books Ngram and
dated back to the last two centuries are studied. It was found out that average
word length slightly increased in the 19th century, and then it was growing
rapidly most of the 20th century and started decreasing over the period from
the end of the 20th - to the beginning of the 21th century. Words which
contributed mostly to increase or decrease of word average length were
identified. At that, content words and functional words are analysed
separately. Long content words contribute mostly to word average length of
word. As it was shown, these words reflect the main tendencies of social
development and thus, are used frequently. Change of frequency of personal
pronouns also contributes significantly to change of average word length. The
other parameters connected with average length of word were also analysed.
