"great, large; much, abundant; a great deal," a dialectal survival of Old English micel, mycel "great, intense, big, long, much, many," from Proto-Germanic *mekilaz (source also of Old Saxon mikil, Old Norse mikill, Old High German mihhil, Gothic mikils), from PIE root *meg- "great." Its main modern form is much (q.v.); the common Middle English form was muchel. The phonetic development of the dialectal survival is obscure and might reflect Old Norse influence. Related: Mickleness. Middle English had muchel-what (pron.) "many various things."
<a href="https://www.etymonline.com/word/splenomegaly">Etymology of splenomegaly by etymonline</a>
Harper, D. (n.d.). Etymology of splenomegaly. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/splenomegaly