nummulation
The arrangement or aggregation of red blood cells into rouleaux, resembling piles of coins.
rare
A marked peculiarity of these bodies is their tendency to cohere immediately after the blood is drawn, thus forming Schultze's grannule-masses, and this process is analogous to the nummulation of the red corpuscules.
Where it comes from
From Latin nummulus (“money”) + -ation. By surface analysis, numm(us) + -ule + -ate + -ion.
Adapted from the Wiktionary entry nummulation (CC BY-SA 4.0).