distinct
The process has three distinct stages.

beginning, early, initial, opening, preliminary
advanced, closing, final, last, late, latter, terminal
Her husband was in the advanced stages of cancer.

halfway (esp. BrE), intermediate, secondary
first, second, etc.
transitional
successive
critical, crucial, formative, important, key, main
a young entertainer at the formative stages of his career

difficult
delicate, vulnerable
life
the different life stages of insects and fish

growth, reproductive
adult, embryonic, juvenile, larval, mature, pupal
experimental, exploratory, testing
committee (BrE,politics), design, development, developmental, formative, planning
The project is still at the planning stage.

knockout (esp. BrE)
Colombia's win sent them through to the knockout stage of the tournament.

quarter-final, semi-final, etc. (esp. BrE)

go through, move through, pass through
The water goes through three stages of purification.

enter, reach
We've entered a crucial stage in the project.

mark, represent
This adaptation represented an important stage in human evolution.

at a/the stage
You should read this article at some stage.

by stages
a process that by stages led to the Cold War

during a/the stage, in a/the stage
in the early stages of the job

in stages
We renovated the house in two stages.

stage in
an important stage in her life

stage of
the latter stages of the race

the beginning of a stage, the end of a stage
Students are tested at the end of each stage of the course.

a stage further, one stage further
take the investigation one stage further

a stage of development, a stage of life

centre/center (often figurative)
A new actress will take centre/center stage in next month's production of ‘The Doll's House’.
He was always unwilling to take centre/center stage.

main
They played the main stage at Glastonbury.

empty
revolving
makeshift
A group of tables were converted into a makeshift stage.

concert
David Bowie returned to the concert stage last week.

political (figurative)
Gore has stepped back onto the political stage.

global, international, national, world (all figurative)
China is now a major player on the world stage.

go on, hit (informal), step on, step onto, take, take to
She was too nervous to go on stage.
I was shaking as I took the stage.
She took to the stage when she was at college.

stand on
jump off, leave, step off
She left the stage to tumultuous applause.

jump on, jump onto
A fan jumped up onto the stage.

return to
share
He once shared the stage with Frank Sinatra.

grace
She is one of the finest actors ever to grace the stage.

set (often figurative)
The thrilling semi-finals set the stage for what should be a great game.

boo sb off
She was booed off the stage.

musical, play, production, show, work
Stravinsky's last stage work

adaptation, version
the stage version of ‘The Lion King’

appearance, performance, role
presence
It was hard to forget her powerful stage presence.

persona
His stage persona was that of a foolish drunk.

name
He adopted the stage name Dixon Hare when he became a full-time actor.

career, debut
She made her stage debut at the age of four.
I began my stage career at the age of ten.

lighting, lights
set
The stage set is the most expensive ever built.

floor
door
Fans hung around the stage door hoping to meet the band.

actor, crew, director, manager, etc.
management
direction
As the stage directions indicate, it is early morning in Moscow.
Shakespeare's famous stage direction: ‘Exit, pursued by a bear.’

left, right
fright
Even experienced actors can suffer from stage fright.

whisper
‘She's pregnant!’ he said in a stage whisper.

the back of the stage, the edge of the stage, the front of the stage, the side of the stage