eternity
I lay there for what seemed like an eternity, unable to move.
The walk home felt like an eternity.
Ten minutes can seem like an eternity when you are hungry.
The six months that she was away felt like an eternity to me.

SMART Vocabulary: related words and phrases

Long periods of time
-athon
a long haulidiom
aeon
age
be in something for the long haulidiom
donkey
eon
epoch
era
eternity
for days, weeks, months, years, etc.
forever
forever and a dayidiom
good
haul
long
long-stay
month
time
yonks