extraconjugal
extracurricular
extra-conjugal
adultery
fornication
criminal conversation
something-something
extramarriage
mistress
number two
sow one's wild oats
free love
nonmarriageable
extramarital sex
kept woman
hetsex
mated
mistressdom
fancy woman
jiggy jiggy
rumpty-tumpty
consummation
sestolet
conjugation
intimate relations
dry sex
jigajig
job
humpa humpa
pareunia
sexual congress
bonky bonky
in-out
marital embrace
throes of passion
boinky
connection
act of darkness
jump someone's bones
know someone in the biblical sense
go to bed with
nonincestuous
sexennary
unincestuous
two-timing
fornicate
hexadactyly
hexadactylism
at it
heterosex