Apparently boards the wife's offspring (7)
I believe the answer is:
stepson
'offspring' is the definition.
(stepson is a kind of offspring)
'apparently boards the wife's' is the wordplay.
I cannot quite understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'wife' could be 'so' (abbreviation for significant other) and 'so' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for stepson that I've seen before include "partner's sprog" , "Child from a spouse's former marriage" , "second family member" , "Male offspring of partner's former marriage" , "younger member of family" .)