All 3 Uses

convention
in
The Perks of Being a Wallflower
(Edited)

I think something like that would be very good for him, especially if the girl were unconventionally beautiful.
p. 51.5

unconventionally = in an unusual way

standard prefix: The prefix "un-" in unconventionally means not and reverses the meaning of conventionally. This is the same pattern you see in words like unhappy, unknown, and unlucky.
I asked my brother if Kelly was unconventionally beautiful.
"No, she's hot beautiful."
p. 81.4
But not in an unconventional way.
p. 131.9 *

unconventional = unusual

standard prefix: The prefix "un-" in unconventional means not and reverses the meaning of conventional. This is the same pattern you see in words like unhappy, unknown, and unlucky.

Definitions:

(1) (convention as in: teacher's convention)
a large conference or meeting
(2) (convention as in: conventional behavior)
something regarded as normal or typical
(3) (convention as in: The Geneva Convention)
a written international agreement
(4) (meaning too rare to warrant focus)