Eje

Eje is so often used figuratively that axis is hardly ever an appropriate choice. Here is the full definition from Orellana:

axis
middle
center line (street, river)
crux, hub, core (argument)
cynosure, center (attraction)
pivotal point (attention, conversation)
main highway
central element
pivot
pivotal figure
crucial or cardinal factor, member, part, person, point, etc.
linchpin
thrust, emphasis, focus, plank
backbone
(aero) hub
(development) corridor

A discussion about eje on a Spanish-English translation list yielded further suggestions from various colleagues (depending on context): issue, pillar, column, dimension, focal point.

Another colleague reminded us that eje also has non-metaphorical meanings. Even so, it's often translated by another word than "axis". He writes:

In my work as a technical translator, mostly oil and gas and other industrial documents, eje means one of two things. Most of the time, it is shaft. This is meaning 4b at dictionary.com:

-4.b A long, generally cylindrical bar that rotates and transmits power, as the drive shaft of an engine.

However, this isn't universal; Mexican writers generally use flecha instead of eje for this object. When they use eje, it almost always means axis:

-1. A straight line about which a body or geometric object rotates or may be conceived to rotate; or, 3, A center line to which parts of a structure or body may be referred.

In Mexico City eje refers very specifically to any road in a system created in the 1970's, in which a number of streets and avenues were widened to provide a grid of north-south and east-west "fast" roads with names that follow the pattern Eje # norte/sur/oriente/poniente (e.g. Eje 2 sur, Eje 4 poniente, etc.) I wondered how I would translate this use of eje. Orellana gives "axle highway" for eje vial, but I don't recognize the term, nor can I find any confirmation of it. A colleague suggested

- arterial (as a noun; no need to make it into an adjective by adding "road" or "avenue")
- trunk road
- boulevard (provided that the context makes it clear exactly what these ejes are).