Mildly comes from mild (Old English milde 'gentle, merciful', from Proto-Germanic *milþijaz, from Proto-Indo-European *meldʰ- 'soft') + -ly. The suffix is part of the word's derivational shape, marking the final grammatical or semantic role while the base supplies the central meaning. As an adverb, it means "to a moderate degree; gently", so the modern sense keeps the older action or relation visible. Relevant historical forms include Old English milde and Proto-Indo-European *meld-. Related words include mild, mildness.