side, edge, beside...

looking from the side, looking aside

listening (to a lecture, hearing, parliament session...

looking on, standing by and watching, sitting back and watching...

supporting role (actor), minor role

side, edge, beside...

interception, monitoring, tapping

roadside

behaving outrageously as though there were no one around, acting without consideration for others, arrogance...

outsider's perspective, as seen by an observer

comrade, friend, associate...

beside, nearby

marginal notes

collateral family, subsidiary line, affiliate...

looking on by an outsider

things overheard

supporting evidence, corroboration

bystander

underline, side line (equivalent to underlining in vertically written text)

marks or dots written alongside a word to indicate stress or draw the reader's attention, emphasis mark, guiding marks written beside kanji to facilitate reading of kanbun

blow received by a bystander, getting dragged in to someone else's fight

marginal notes, side notes, gloss

marginal notes, side notes, gloss

(theatrical) aside

branch (of a river), tributary, branch...

subtitle (e.g. of a book)

side road, byroad, digression (e.g. from argument)

digression, dicta, dictums

from outside, from the side

near, close, beside...