modal (adj.)

"pertaining to or affected by a mode," 1560s, originally a term in logic, from French modal and directly from Medieval Latin modalis "of or pertaining to a mode," from Latin modus "measure, extent, quantity; proper measure, rhythm, song; a way, manner, fashion, style" (in Late Latin also "mood" in grammar and logic), from PIE root *med- "take appropriate measures." Musical sense is from 1590s; In grammar from 1798.

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Definitions of modal from WordNet
modal (adj.)
relating to or constituting the most frequent value in a distribution;
the modal age at which American novelists reach their peak is 30
Synonyms: average
modal (adj.)
of or relating to a musical mode; especially written in an ecclesiastical mode;
modal (adj.)
relating to or expressing the mood of a verb;
modal auxiliary
modal (n.)
an auxiliary verb (such as `can' or `will') that is used to express modality;
Synonyms: modal auxiliary verb / modal auxiliary / modal verb