Where does the expression "a wide berth" come from
the first definition for "berth" given in the Oxford English Dictionary is
- Naut. ‘Convenient sea-room, or a fit distance for ships under sail to keep clear, so as not to fall foul on one another’
with examples from 1622.
The OED says of the word's etymology:
A nautical term of uncertain origin: found first in end of 16th cent. Most probably a derivative of bear v.1 in some of its senses: see especially sense 37, quot. 1627, which suggests that berth is = ‘bearing off, room-way made by bearing-off’; compare also bear off in 26 b. The early spellings byrth , birth , coincide with those of birth n.1 ‘bearing of offspring, bringing forth,’ but it is very doubtful whether the nautical use can go back to a time when that word had the general sense ‘bearing’; it looks more like a new formation on bear, without reference to the existing birth.
So the word berth is very likely closely related to birth; but this meaning is far removed from it.
'Berth' originally meant 'a place where there is sea room to moor a ship' which in turn was derived from 'bearing off'. So when sailors where asked to keep a wide bearing off something, they were asked to make sure there was enough sea room from it.
From here, when accepted to general population, its meaning also became more general as in 'keep more distance from'.
http://www.phrases.org.uk/meanings/wide-berth.html
Maybe this is just obvious, but the one part that no one's yet mentioned is why you'd want a wide berth: because (some) ships are heavy, slow-moving and unwieldy conveyances, especially compared to wagons, carts, horses, etc. With a narrow berth the ship or pier or other ships could be easily damaged, and generally there is a greater risk of loss of control of the situation.
So it makes sense, then, that we urge people to give a wide berth, metaphorically, to other people that are unwieldy, out of control, generally uncontrollable, potentially dangerous, have a 'short fuse' or low anger threshold, etc.