The fun part is that
ratlin,
ratline, or
ratling is not about rodents.
Displaying the etymology takes a wee bit of effort.
If we stick with
English for the nonce, the key
events to note are:
* in the 15th century,
ratling is used as the name for a particular type of cordage, namely three-strand laid hemp
rope, usually tarred, of a medium dimension (fatter than 'small stuff' but much thinner than 'cable').
* by the early 17th century,
ratlings were the cordage steps made to the shrouds and then used as ladders by which mariners climbed high in the
rigging.
As with many of the nautical words in
English, the origins are best described as North Sea sailing vocabulary - a vocabulary shared by sailors working on the same sea and from time to time using the same
ports and boats regardless of 'national' identity.
The immediate ancestors of early 15th century
ratling are not neatly preserved on parchment. North Sea sailors' speak was an oral language, not a written one.
The etymologists fingers all point in one general direction in this case (dinnae be confused by the initial dual nature of the one direction): to (1) Old French, about 1150, and the word
raelingue, the cordage used as bolt rope to reinforce the edges of
sails or the edges of
fishing nets; and (2) Norman-French/Channel Islands French (undated, because it was not writtne down with a date of publication)
rar-lik, the cordage used as bolt rope to reinforce the edges of sails or the edges of
fishing nets.
Your copy of
Dictionnaire de L’Academie Francaise will like mine take you unerringly to the same point of origin agreed among the wise heads gathered around the table: Old Norse
rar-lik, the reinforced edge of a sail attached to a yardarm.
That exposes the components as Old Norse
rar or
ra, a spar, an oar, a sail-yard; and Old Norse
lig or
lik a bolt rope, a line, cordage.
Anyone paying attention so far will see that
lig or
lik is the same as the word
leech, currently used for the after edge of a fore-and-aft sail. And know that the predecessor is proto-Germanic
lika, a band or binding (that joins or holds things together), a joint of an arm or a leg (think of
ligament), an articulation; derived from the proto-Indo-European
leyg,
leig, to bind, to tie.