> I wonder if 'fecht' is related to English 'fight'.
"Stair an Fhocail" (féach "feasta" sa chartlann):
Tháinig "fecht" agus an focal Breatnaise "gwaith" (= obair)
ó * wekto- nó *wektâ- sa Chomh-Cheiltis, a shíolraigh ón
bhfréamh Ind-Eorpaise *wegh- (téigh, iompair i bhfeithicil).
Tá na focail seo gaolmhar le "way" agus "wag(g)on" i mBéarla,
agus le "via" i Laidin.
> And did the word originally refer to an expedition for war,
> and these expeditions were so common in ancient Ireland that
> the word came to mean any kind of occasion or journey?
Rather the other way around. The meaning "journey" would be
primary, etymologically, but so many expeditions were warlike,
as you point out, that the meanings "raid, hosting, assault,
fight" developed. The earliest examples of "fecht" I know of
are in the Wb. Glosses. Mostly we get the temporal idiom "in
fecht-so" = "now", but there is a single instance of the word
used to mean "journey, expedition", specifically the journey
of the Jews out of Egypt: "hore rombu thoissech na fectae
= because he (Moses) had been the leader of the expedition".