Meaning

• An attack; an assault especially of an army.

• The initial phase of a disease or condition, in which symptoms first become apparent.

  "the onset of schizophrenia"

• The initial portion of a syllable, preceding the syllable nucleus.

• (acoustics) The beginning of a musical note or other sound, in which the amplitude rises from zero to an initial peak.

• A setting about; a beginning.

  "the onset of puberty"

• Anything added, such as an ornament or as a useful appendage.

Meaning

• To assault; to set upon.

• To set about; to begin.