There are two special words (abbreviations) showing the significance (weight) of a bit in a set (nibble): lsb - least significant bit, msb - most significant bit. Both "lsb" and "msb" are not general English words therefore that abbreviations could be unambiguously distinguished among other words within sentences.

Similarly, i search for a pair of terms for first and last [bit transmitted] on wire, i.e. defining the transmission order of a bit in a set. And if with first-on-wire - abbreviated as fow - i see no trouble because "fow" is not a common English word (as Google Translate assures me), abbreviating of last-on-wire results in the well-known word "low" which could rise disambiguations.

Google Translate gives a rare (as i assume) synonym for the word "last" - the word "dernier" (adj.) that results in dernier-on-wire - dow - not a common English word now. Then fow:dow seems as a good variant. But...

1) Is it correct? (i am not native speaker, it's difficult to me to understand such by myself.)

2) Is (are) another synonym(s) for the adj. "last" (and for the "first") known/used as more comfortable/relevant in this case? (whose abbreviations also must/should not intersect with general/common English words.)

Beforehand thanks.

"Ultimate" fits both your criteria as a replacement for "last" and won't be confused with a common English word..."UOW"

Per the Google Dictionary, ultimate, in this sense, is defined as:

adjective: ultimate

1. being or happening at the end of a process; final.

Example: "their ultimate aim was to force his resignation"

I perused the synonyms but sadly, "concluding" and "terminal" would spell "COW" or "TOW", both common English words

Best and most common:

Former & Latter

You may abbreviate "former" as "fmr." and "latter" as "ltr.".

That is one of the best and most common set of synonyms used in place of "first" and "last". Though they are not precisely interchangeable, they work in many situations.

Consider this article.

Alternatively, if you need to be irregular and create something special or more concise, consider FST & LST:

1. FST is proper

"FST" is a proper abbreviation for "first", so "LST" naturally fits for readers, even with no prior knowledge, merely by the juxtaposition.

2. Use uppercase, not lowercase (in this situation)

Using lowercase letters would be a bad idea because in many serif and Roman fonts the "l" (L) looks like a "1" (one) so "lst" (LST) looks like "1st" (1 ST).

3. Don't punctuate (in this situation)

Don't use a period because then "last" has the same number of characters as "lst."; using capital letters would clear this up.