Wife is a printer? Shows she's not being serious (5)
I believe the answer is:
winks
'shows she's not being serious' is the definition.
(winking shows that you're only joking)
'wife is a printer?' is the wordplay.
'wife' becomes 'w'.
'is a printer?' becomes 'inks' (ink can mean to print with ink).
'w'+'inks'='WINKS'
(Other definitions for winks that I've seen before include "Flashes; tiddly- - -" , "Closes and opens one eye as signal" , "See 18" .)