Related to the notion of limit and threshold, limen opens up a slightly different semantic field. Its etymology is related to the Latin limus that means “transverse, oblique”. The Latin noun limen, liminis is usually translated as “1. threshold, doorstep, sill; 2. lintel; 3. entrance, doorway, approach; 4. house, home, abode, dwelling; 5. beginning, commencement; 6. end, termination” (cf. http://en.wiktionary.org/wiki/limen). It includes a movement like crossing or passing and alludes to a certain danger whilst doing so.
“In physiology, psychology, or psychophysics, a limen or a liminal point is a threshold of a physiological or psychological response. Liminal, as an adjective, means situated at a sensory threshold, hence barely perceptible. The absolute threshold is the lowest amount of sensation detectable by a sense organ.” (http://en.wikipedia.org/wiki/Limen)