aamu.

Unknown. The word is known to be recent, as the original word for morning in Finnish is huomen. It is likely that once huomen began to be used in words meaning "tomorrow", such as huominen and huomenna, it was eventually replaced by aamu in the sense "morning". One theory is that aamu is a shortening of the archaic word *huomenhaamu (“morning twilight, morning mist”), which is a compound of huomen (“morning”) + haamu (“twilight, mist, ghost”), but no such compound is attested in older texts, which leaves this theory uncertain. Another theory is that the word is borrowed from the genitive form of Old Swedish *āma (“mist, smoke”) (whence dialectal Swedish åmme), which would have developed the sense "daybreak". While this could be compared to the possible development of aurinko (“sun”) < auer (“haze”), it is likewise uncertain.