Hello Pali friends,
The expression 'ekāyana maggo' is used in Satipatthana formula, Mahasihanada sutta, three Jatakas, and explained in Niddesa.
In Mahasihanada Sutta (MN I 74) this term is used with the meaning "leading to only one place":
37. (1) "By encompassing mind with mind I understand a certain person thus: 'This person so behaves, so conducts himself, has taken such a path that on the dissolution of the body, after death, he will reappear in a state of deprivation, in an unhappy destination, in perdition, in hell.' And then later on, with the divine eye, which is purified and surpasses the human, I see that on the dissolution of the body, after death, he has reappeared in a state of deprivation, in an unhappy destination, in perdition, in hell, and is experiencing extremely painful, racking, piercing feelings. Suppose there were a charcoal pit deeper than a man's height full of glowing coals without flame or smoke; and then a man scorched and exhausted by hot weather, weary, parched and thirsty, came by a path going in one way only
and directed to that same charcoal pit. Then a man with good sight on seeing him would say: 'This person so behaves, so conducts himself, has taken such a path, that he will come to this same charcoal pit'; and then later on he sees that he has fallen into that charcoal pit and is experiencing extremely painful, racking, piercing feelings. So too, by encompassing mind with mind... piercing feelings.http://www.accesstoinsight.org/canon/su ... mn012.html
If we apply the same meaning to Satipatthana sutta usage, then the meaning would be 'leading to only one place (Nibbana) [and no other place]'.
Atthakatha (Commentary) to Satipatthana sutta (see English translation by Soma Thera below) gives five meanings, which includes (in translation of Rupert Gethin):
1) eka-maggo aya.m bhikkhave maggo na dvedhaa-patha-bhuuto ti eva.m attho da.t.thabbo
(this path is a path to one (destination), not a forked path)
2) ekena ayitabbo
(a path that is ekāyana is one to be travelled alone)
3) ekassa ayano ekāyano; ekassā ti seṭṭhassa; sabba-satta-seṭṭho va bhagavā
(the ekāyana path is the path of 'the one' in the sense of 'the best', which means 'the best of all beings', namely the Buddha)
4) ayatī ti va ayano; gacchati gacchati pavattatī ti attho; ekasmiṃ ayano ti ekāyano
(an ekāyano path is a path that occurs or is found in just one place; in the present context that is in the dhamma-vinaya of the Buddha)
5) eka.m ayatii ti ekaayano
eka.m nibbaana.m eva gacchatii ti vutta.m hoti
(a path that is ekaayana is one that goes to one place only, namely Nibbana)
The three Jataka usages are:
Ja IV 349:
sūkarehi samaggehi vyaggho ekāyane hato ti
Atthakatha explains is as: 'tattha ekāyane hato ti eka-gamasmiṃ yeva hato' - 'The tiger was killed at one charge by the pigs en masse.'
In Jaat. 524:
ekaayane ta.m pathe addasaasi.m balena va.n.nena upeta-rupa.m
One can just make guesses about this verse (Ja V 172-3) since it's not explained neither in the text nor in Atthakatha to this passage.
In Jaat. 537 (Ja VI 557):
2194. “Ekaayano ekapatho, saraa sobbhaa ca passato;
a~n~na.m magga.m na passaami, yena gaccheyya assama.m.
In the Atthakatha to this verse it is explained as narrow path:
Ekaayanoti ekasseva ayano ekapadikamaggo.
To complete the picture, here is Niddesa explanation, from "The Buddhist Path to Awakening" by Rupert Gethin:
"Interestingly though, the late canonical Niddesa does extend the application of the term ekaayana-magga to all seven sets. The Niddesa comments that the Blessed One is eka because because he has travelled the ekaayana-path (bhagavaa ekaayana-magga.m gato ti eko) and then goes on to explain the ekaayana-path as 'the four extablishings of mindfulness, the four right endeavours, the four bases of success, the five faculties, the five powers, the seven awakening-factors, the noble eightfold path' (Nidd I 455-6). The Niddesa then quotes the following verse:
Seeing the end and destruction of birth, he knows the ekaayana-path in friendliness and compassion; by this path they crossed the flood in the past, they will cross [it in the future] and they cross [it now].
(This verse is also found at S V 168, 186, and is quoted at Sv III 745, Ps I 230.)
So it is, says the Niddesa, that the Blessed One is eka because he has travelled the ekaayana-path (eva.m bhagavaa ekaayana-magga.m gato ti eko). At the same time as extending the term ekaayana-magga to all seven sets, the Niddesa also preserves a tradition of the term's special association with sati or 'mindfulness': 'that which is mindfulness, recollection ... the awakening-factor of mindfulness, the ekaayana-path - this is called mindfuless.' (Nidd I 10, 347, 506)"