Please note that the terms 'tetragram' (a word consisting of
four letters, from the greek tetragrammaton, refering to the name of
god usually transliterated as YHWH) and 'pentagram' (a geometric
figure) you find listed in your dictionary do not refer to n-grams.
So if a new term has to be coined we might follow logical arguments.
Regards
Markus Schulze
max@linguistik.uni-erlangen.de