Etymology

According to one source, the origin of this phrase is from the cloth industry, where a small flaw in a fabric would be marked by a string so it could easily be spotted. This suggests a meaning of "without flaws".

In ancient times, documents that were written on parchment had strings that were used to tie them shut, after they were rolled up. The Babylonian Talmud in Tractate Bava Metzi'a mentions an example of a man who gives his wife a get (bill of divorce) with a string attached, but holds on to the string, so that he can snatch it back (apparently because he is unwilling to actually give her a divorce). According to Jewish law, this is not a valid divorce, because the man has not properly delivered the get, by freely giving it to his wife.

Adverb

1. Without conditions or obligations; without a catch.

   For a friend, I'll help out for free, no strings attached.