Experimental shelter took in about four (9)
I believe the answer is:
tentative
'experimental' is the definition.
(I've seen this before)
'shelter took in about four' is the wordplay.
'shelter' becomes 'tent' (tent is a kind of shelter).
'took in' becomes 'ate' ('eat' can be a synonym of 'take in').
'about' is an insertion indicator.
'four' becomes 'iv' (roman numeral).
'ate' enclosing 'iv' is 'ative'.
'tent'+'ative'='TENTATIVE'
(Other definitions for tentative that I've seen before include "To be confirmed" , "Experimental" , "Cautious - provisional" , "Diffident" , "Hesitant; not certain" .)