Eccentric people generally take on board wedding vow (6)
I believe the answer is:
'eccentric' is the definition.
(I've seen this before)
'people generally take on board wedding vow' is the wordplay.
'people generally' becomes 'we' (I can't explain this - if you can you should believe this answer much more).
'take' becomes 'r' (abbreviation for 'recipe', Latin for 'take').
'on board' means one lot of letters goes inside another (inserted letters are taken on board).
'wedding vow' becomes 'I do' ('I do' is part of the traditional wedding vows).
'r' going within 'ido' is 'irdo'.
Can you help me to learn more?
(Other definitions for weirdo that I've seen before include "Person who behaves bizarrely" , "Slang for odd or eccentric person" , "strange character" , "Freak" , "Derogatory term for an eccentric" .)