Modicum
late 15th century: from Latin, neuter of modicus ‘moderate’, from modus ‘measure’.
wiktionary
From Late Middle English modicum, borrowed from Latin modicum(“a little, a small amount”), a noun use of the neuter form of modicus(“moderate; restrained, temperate; reasonable”) + -cum(suffix forming neuter nouns). Modicus is derived from modus(“a measure; a bound, limit”) (ultimately from Proto-Indo-European *med-(“to measure”)) + -icus(suffix meaning ‘of or pertaining to’ forming adjectives). [1]
The plural form modica is derived from Latin modica.
etymonline
modicum (n.)
"small quantity or portion," late 15c., Scottish, from Latin modicum "a little," noun use of neuter of modicus "moderate, having a proper measure; ordinary, scanty, small, few," from modus "measure, extent, quantity; proper measure," from PIE root *med- "take appropriate measures."
