user471: The following phrase comes from DN 13:

“ayameva ujumaggo, ayamañjasāyano niyyāniko niyyāti takkarassa
brahmasahabyatāya, yvāyaṃ akkhāto brāhmaṇena pokkharasātinā”ti.

T.W. Rhys Davids translated here as:

‘This is the straight path, this the direct way which makes for
  salvation, and leads him, who acts according to it, into a state of
  union with Brahmā. I mean that which has been announced by the Brahman
  Pokkharasādi.’

Bhikkhu Sujato translated here as:

“This is the only straight path, the direct route that leads someone
  who practices it to the company of Brahmā; namely, that explained by
  the brahmin Pokkharasāti.”

What does "brahmasahabyatāya" mean? What does "sahabyatāya" mean?
This translation could be meaningful. "Union with Brahman" sounds like the modern Hindu concept of Moksha which is a union with God or Ultimate Reality. On the other hand, "company of Brahma" sounds like rebirth into the Brahma realm. What's the correct interpretation?

user43: This topic is thoroughly analyzed in a 2013 paper “Brahmanical Terminology and the Straight Way in the Tevijja Sutta" by Brett Shults.
There, Shults explains that "sahaya" means "friend", "companion" - therefore "sahavyata" means "companionship" or "fellowship".
Shults explains (as ChrisW said too) that the term refers to the Brahman's idea of The Goal, which Buddha then takes and clarifies according to the Buddhist proper interpretation.
Shults also argues that the meaning of the word is most probably "joining", "in a sense as we might speak of joining a club".
I personally think "sahaya" means something more like "sidekick" or "henchman" - i.e. someone who is always together with, but is "lesser" than, the main figure. The idea IMO is that one is in a state of joining with Brahma without actually being Brahma.

user254: In DN 13 the term is originally used by Brahmins talking with each other, and so between them it meant whatever (non-Buddhist doctrine) they each understood it to mean.
At the end of the sutta the Buddha teaches them the four brahmaviharas and defines or explains that these are the path to "companionship with Brahma" -- i.e. I think he thus redefines brahmasahabyatāya (whatever it used to mean) in Buddhist terms, in a way that can be understood and agreed by the Brahmins.

471: <p>The following phrase comes from DN 13:</p>

<blockquote>
  <p>“ayameva ujumaggo, ayamañjasāyano niyyāniko niyyāti takkarassa<br>
  <strong>brahmasahabyatāya</strong>, yvāyaṃ akkhāto brāhmaṇena pokkharasātinā”ti.</p>
</blockquote>

<p>T.W. Rhys Davids translated <a href="https://suttacentral.net/dn13/en/tw_rhysdavids" rel="nofollow noreferrer">here</a> as:</p>

<blockquote>
  <p>‘This is the straight path, this the direct way which makes for
  salvation, and leads him, who acts according to it, into a state of
  <strong>union with Brahmā</strong>. I mean that which has been announced by the Brahman
  Pokkharasādi.’</p>
</blockquote>

<p>Bhikkhu Sujato translated <a href="https://suttacentral.net/dn13/en/sujato" rel="nofollow noreferrer">here</a> as:</p>

<blockquote>
  <p>“This is the only straight path, the direct route that leads someone
  who practices it to the <strong>company of Brahmā</strong>; namely, that explained by
  the brahmin Pokkharasāti.”</p>
</blockquote>

<p>What does "brahmasahabyatāya" mean? What does "sahabyatāya" mean?</p>

<p>This translation could be meaningful. "Union with Brahman" sounds like the modern Hindu concept of Moksha which is a union with God or Ultimate Reality. On the other hand, "company of Brahma" sounds like rebirth into the Brahma realm. What's the correct interpretation?</p>
 43: <p>This topic is thoroughly analyzed in a 2013 paper “Brahmanical Terminology and the Straight Way in the Tevijja Sutta" by Brett Shults.</p>

<p>There, Shults explains that "sahaya" means "friend", "companion" - therefore "sahavyata" means "companionship" or "fellowship".</p>

<p>Shults explains (as ChrisW said too) that the term refers to the Brahman's idea of The Goal, which Buddha then takes and clarifies according to the Buddhist proper interpretation.</p>

<p>Shults also argues that the <em>meaning</em> of the word is most probably "joining", "in a sense as we might speak of joining a club".</p>

<p>I personally think "sahaya" means something more like "sidekick" or "henchman" - i.e. someone who is always together with, but is "lesser" than, the main figure. The idea IMO is that one is in a state of joining with Brahma without actually being Brahma.</p>
 254: <p>In DN 13 the term is originally used by Brahmins talking with each other, and so between them it meant whatever (non-Buddhist doctrine) they each understood it to mean.</p>

<p>At the end of the sutta the Buddha teaches them the four brahmaviharas and defines or explains that these are the path to "companionship with Brahma" -- i.e. I think he thus redefines <em>brahmasahabyatāya</em> (whatever it used to mean) in Buddhist terms, in a way that can be understood and agreed by the Brahmins.</p>
