Comitia is indeed derived from comes. Both come from the prefix com- "with, together" plus the root i- "go": a companion is someone who goes with you, and an assembly is a place where people go together.
Here's the entry from de Vaan's etymological dictionary of Latin:
Does Latin allow the letter k in suffixed words?
It doesn't, because Latin doesn't allow the letter K at all.
Well, almost; there are a couple of words with K and they mostly have spelling variants with C.
In particular, the words you mention are never spelled with a K in Latin.
I have never seen K within a Latin word, only at the beginning.
(Perhaps there ...
The word epitope was coined by Niels Kaj Jerne in 1960. He defined the term as:
"surface configurations, single determinants, structural themes,
immunogenic elements, haptenic groups, antigenic patterns, specific
(Aalberse RC, Crameri R. "IgE‐binding epitopes: a reappraisal". Allergy 2011; 66: 1261–1274.)
It is the place on the surface of ...
I take it you're not interested in later words like sultanus, algebra, alcohol or nadir. Then I hope that this article from 1892 isn't too outdated: 'On Semitic Words in Greek and Latin' by W. Muss-Arnolt (https://www.jstor.org/stable/2935792?seq=1#metadata_info_tab_contents). If you search for "lat." within the pdf, or look in the index at the end, you'll ...
I just recently stumbled across two examples in Lewis and Short of semitic words, for which L&S cites no Greek intermediary. Of course, the lack of citation itself is not exactly proof that Greek intermediaries do not exist.
The two words are manzer from the Hebrew, and mapālia from the Punic, conveniently located adjacent to each other on the page.
Regarding the shift from "folding" to "returning" Sp. Llegar, wiktionary has some interesting comments: "The semantic shift over time from "to fold" is also found in some other Romance cognates, and may be linked to the idea of folding sails when arriving at a port, especially in Iberian Romance where naval tradition was strong. Compare Portuguese chegar; ...