I’d invested in speculative deal for bathroom fitment (5)
I believe the answer is:
bidet
'bathroom fitment' is the definition.
(I've seen this before)
'i'd invested in speculative deal' is the wordplay.
'invested in' means one lot of letters goes inside another.
'speculative deal' becomes 'bet' (I can't justify this - if you can you should believe this answer much more).
'id' inserted within 'bet' is 'BIDET'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for bidet that I've seen before include "Washing facility" , "Bathroom fixture" , "Bathroom appliance" , "Bathroom item" , "bathroom accessory" .)