prep.
&
adv.
-
[as prep.]
on the subject of; concerning.
- used to indicate movement within a particular area or location in a particular place.
-
[as adv.]
approximately.
Phrase
- be about to
be on the point of. - know what one is about
informal be sensible and self-possessed.
Etymology
OE onbūtan, from on ‘in, on’ + būtan ‘outside of’ (see but2).