Poorly cow in house for what reason? (3,4)
I believe the answer is:
how come
'what reason?' is the definition.
I can't tell whether this defines the answer.
'poorly cow in house' is the wordplay.
'poorly' indicates anagramming the letters (I've seen this in other clues).
'in' means one lot of letters goes inside another.
'house' becomes 'home' (homing is a kind of housing).
'cow' with letters rearranged gives 'owc'.
'owc' inserted into 'home' is 'HOW COME?'.
'for' is the link.
Can you help me to learn more?
(Other definitions for how come that I've seen before include "Explain why" , "What's the reason" .)