tword is 10 bytes, I think t means t.en

but fword and pword are 6 bytes,

why f and p ?

if it were 5 bytes then f.ive and p.enta,

or is it like XP drive letters where you run out of options?

"tword" comes from the "temporary" (as in "temporary real format").
"fword" and "pword" are for "far pointer" or just "pointer".

To me fword sounds more like the far-word and pword the pointer-to-word sizes !