Germanic Lexicon Project
The word 7 is only one character long. All one-character words are considered stopwords, i.e. high-frequency words which aren't indexed and can't be searched for.
7 is not in the list of known abbreviations in Cleasby/Vigfusson. If it really is an abbreviation, please click here to report it.
Modern English: Search ARTFL's Gutenberg Webster for 7
Modern German: Search Leo for 7