Tax department underwriting American shows (4)
I believe the answer is:
airs
'shows' is the definition.
(shows on TV)
'tax department underwriting american' is the wordplay.
'tax department' becomes 'IRS' (Internal Revenue Service, US government dept).
'underwriting' says to put letters next to each other (some letters written underneath others).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'irs' after 'a' is 'AIRS'.
(Other definitions for airs that I've seen before include "affectation of superiority" , "feelings" , "Ventilates, say grievances" , "Pretentiousness" , "Haughty affectation" .)