<Regarding citta-gu, it is similarly formed as paara,guu etc. I think
<-GUU can mean either
<(1) literally, "gone" as in Paara,guu (gone across), that is,
crossed over
<suffering, doubt, etc.
Actually, citta-gu is not similarly formed as paara-gu. The meaning
('having spotted cows': cittaa gaavo yassa) makes that clear. To
take it as so formed makes it hard to assign a meaning to the word.
If we still doubt the meaning `having spotted cows' we can compare
the identical compound (citra-gu, with the common phonological
variation of tra for Pali tta) used in a Sanskrit text (Bhaagavata
Puraa.na x.61.13 as the name of a son of Krishna), which is
translated as `having bridled cows'. In any case, what reason is
there to doubt the given meaning?
One may ask, what then is gu? It is obviously the unaccented or
weak form of go. The word go and its derivative gava occur with
extreme frequence in Indo-Aryan languages, reflecting the fact that
cattle rearing was a favourite occupation of the early (self-styled)
Aryans. It has always been explained as a word going back to Indo-
European. Cognate words are Greek bous, Latin bovii (from which
English `bovine') Armenian kov, German Kuh (compare English `cow'),
Avestan gaaus etc. etc. Apparently the original IE word had an
initial guttural-labial pronounciation, something like kw, of which
Indo-Iranian/Indo-Aryan retained the guttural k/g element only,
while some other languages retained the labial only. (This is of
course a simple layman's explanation. showing my elementary grasp of
a complex linguistic phenomenon.)
When we understand the gradation au/o/u as the three levels of the
same vowel, many problems of grammar in Pali and Sanskrit disappear.
Vowel gradation (or ablaut) was of course known to ancient
grammarians who used the terms gu.na (middle or normal grade) and
v.rddhi (strong grade) in dealing with the phenomenon. They did not
use a specific technical term for the weak grade, apparently
assuming the so-called weak grade to be the normal grade. We have
the strong grade vowel in the form gaavo (nom. pl.), the middle
grade in gona.m (gen. pl.) and the weak grade in this form gu- This
form of course occurs rarely, both in Sanskrit and Pali, whence
probably the misunderstandings.