Chief support provided by mother during visit (8)
I believe the answer is:
mainstay
'chief support' is the definition.
(I've seen this before)
'by mother during visit' is the wordplay.
'by' says to put letters next to each other.
'mother' becomes 'ma' (ma is a kind of mother).
'during' becomes 'in' (I've seen this in other clues).
'visit' becomes 'stay' (I've seen this before).
'ma' next to 'in' is 'main'.
'main'+'stay'='MAINSTAY'
'provided' acts as a link.
(Other definitions for mainstay that I've seen before include "Linchpin, principle support" , "Rope to the mast is the chief support" , "Piece of rigging" , "Strongest support" , "Chief support, like mast cable" .)