All 3 Uses

convention
in
The Hunt for Red October
(Auto-generated)

He has a doctorate in engineering from MIT, and he knows how to think unconventionally.†
Chpt 4. *

unconventionally = in a manner that is not normal or typical

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.
This could be the beginning of a conventional war against NATO, its first step being interdiction of the sea lines of communication.†
Chpt 6.
The international basis for this is the Salvage Convention of 1910 (Brussels), which codified the transnational nature of admiralty and salvage law.†
Chpt 9.

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)