'Tabu', also spelled 'taboo' works here...
swearing, cursing
turn
wits
The "f word" is a four-letter word, originally meaning a sex act, but used in many ways, including swearing or cursing. (for spelling or origin see related questions)
Yep, an act.
act
do
The four-letter word that means to be alive is "live." It can refer to the state of being alive or to the act of living, and is often used in various contexts, such as in music or events that are happening in real-time.
Sin.
act
act
act