Evenly means in equal amounts, or at a steady rate. Spread evenly, divided evenly, breathing evenly.
In cooking it is one of the most repeated instructions: spread evenly, distribute evenly, cook evenly — because uneven heat is what ruins things. Of division it means in equal shares. Of breathing or movement it means steady rather than equal. Note evenly matched, which is the fixed phrase for a contest where neither side has an advantage.
1adverbevenlyIn equal amounts.
“Share the sweets evenly so that everyone gets the same number.”
2adverbsteadyAt a steady rate.
“The baby was finally asleep, breathing slowly and evenly.”
evenly is a manner of equality or steadiness.
Old English efenlice is even plus -ly. Even has meant both level and equal since Old English, which is why evenly does two jobs.
Old English
efenlīċe — evenly, alike, equally
Middle English
evenly
English, today
evenly
From Middle English evenly, evenliche, from Old English efenlīċe (“evenly, alike, equally”), equivalent to even + -ly.
Etymology from Wiktionary, CC BY-SA