Where does “lymphaticovenous” come from?

lymphaticovenous (English) comes from English venous, from Latin venosus, from Latin -ōsus, from Old Latin -ōssus.

Ancestry of “lymphaticovenous”, step by step

Step	Language	Word	Meaning
1	English	venous	Of or pertaining to veins; Possessing veins;...
2	Latin	venosus	full of veins, venous; dry, meagre
3	Latin	-ōsus	ose, -ous, -ful (full of or overly prone to)
4	Old Latin	-ōssus	—