In his commentary of MN 49, Ven. Thanissaro wrote:
It is a play on the word brahma, which is not only a noun denoting the
highest levels of devas, but also an adjective meaning "of great or
MN 49 is entitled the "Brahma invitation", so Ven. Thanissaro says that it means firstly an invitation by the Brahma, but it also means (through a word play) an invitation of great power or high power, which is an invitation by the Buddha to Mara (the personification of the temptation of sensual enjoyments and becoming) to refute the Buddha's claim that he has put an end to becoming once and for all.
An allegorical use of the term "Brahma" can be seen elsewhere. For e.g. parents are like the "Brahma" to their children in Iti 106 and the Buddha himself is like the "Brahma" to his disciples in Iti 100, who are "born from his mouth".
In Iti 112, we see the statement "he set the Brahma-wheel going". What is Brahma wheel? Ven. Thanissaro comments that it refers to the Dhamma wheel of SN 56.11:
The Brahma-wheel = the Dhamma-wheel, the name of the Buddha's first
sermon, so called because it contains a "wheel" that lists all twelve
permutations of two sets of variables: the four noble truths — stress,
its origination, its cessation, and the way leading to its cessation —
and the three levels of knowledge appropriate to each truth: knowledge
of the truth, knowledge of the task appropriate to the truth, and
knowledge that the task has been completed. This wheel constitutes the
Buddha's most central teaching.
Here, calling the Dhamma wheel "Brahma wheel" denotes that it is the Great Wheel.
The most interesting use of this phrase comes in Iti 68:
One whose passion, aversion, & ignorance
are washed away,
is said to be
composed in mind,
one for whom fear & hostility
one who's abandoned
Here's the Pali version from here:
“Yassa rāgo ca doso ca,
avijjā ca virājitā;
So the Tathagata is awakened (buddham) and became Brahma (brahmabhūtaṃ).
In other words, he became great, like a god to us.
Returning back to MN 49, the opening verse states:
Now on that occasion an evil viewpoint had arisen to Baka-Brahma:
'This is constant. This is permanent. This is eternal. This is total.
This is not subject to falling away — for this does not take birth,
does not age, does not die, does not fall away, does not reappear. And
there is no other, higher escape.'
Ven. Thanissaro's footnote reads:
Baka Brahma here appears to be referring both to his Brahma world and
to the state of mind that enables one to inhabit his Brahma world.
So, this points to Brahma as referring to states of mind and being (or becoming - bhava) which are of great and high power.
The sutta shows that such a mind state and state of being is not permanent or eternal, and there are even higher states of mind and being.
So, we can say that this is the "subtle" interpretation of Brahma.