We now use this word only in reference to the current sense of the verb to garble: to reproduce some message or information in a confused or distorted way. But that’s a long way from its first sense in English. The word ultimately derives, through Arabic and Italian, from Latin cribrum, a sieve.
Garble was a technical term in medieval commerce throughout the Mediterranean, mainly within the spice trade. A garbler was a person whose job was to sieve spices to remove the rubbish from them, the garble then being the rubbish itself. It appears for the first time in English in Richard Hakluyt’s work The Principal Navigations, Voyages and Discoveries of the English Nation in 1599.
In the next century the verb was applied to various figurative kinds of sifting, such as the weeding out of unfit persons from an organisation (so a writer during the Commonwealth period in Britain in 1650 was able to issue the recommendation that “His army must be garbled”). It was also applied to a process by which coins were inspected for quality. That’s where part of the transition to the modern sense seems to have taken place. The coin sifting was done as a form of counterfeiting: the good ones were melted down for their precious metal content, while the rubbish was put back into circulation.
You can see how that could lead, as it actually did, to the next sense of the verb — the idea of selecting material mischievously in order to misrepresent what somebody said. Today we don’t usually imply malicious intent when we say something has been garbled in transmission and the idea of sieving or of conscious selection has vanished.