fair, good, reasonable, safe
April is a safe guess for first deliveries.

educated, informed
She could make an educated guess as to what was wrong with him.

rough, wild
At a rough guess, I'd say we're about twenty miles from home.

correct, lucky
‘How did you know?’ ‘It was just a lucky guess.’

first, initial

have (BrE), hazard, make (BrE), take (AmE), venture (esp. AmE)
If you don't know the answer, have/take a guess.
If I might hazard a guess …
If I had to venture a guess, I'd say this was painted in the 1890s.

give sb
‘Where's Tom?’ ‘I'll give you three guesses!’

be correct, be right

at a guess
At a guess, I'd say there's a problem with the fuel pump.

guess about, guess as to, guess at
He made a wild guess as to how much the piano might cost.

sb's best guess
What's your best guess on what's going to happen?

a guess based on sth
a guess based on your experience

correctly, right
incorrectly, wrong
Jane had guessed wrong about who was responsible for the fire.

easily
an easily guessed password

can
Can you guess his age?

can only
We can only guess how fast a dinosaur might have run.

try to
be easy to, not be difficult to, not be hard to
It's not hard to guess where they went.

at
I was only guessing at her age.

from
She guessed from his expression that he had not won.

could have guessed, might have guessed, should have guessed
So it was Rob who broke the window? I might have guessed!

guess again
That's not the answer. Guess again.
If you think I'm lying, well guess again.

if you haven't already guessed
If you haven't already guessed, I'm going out with Steve.

I guess so, I guess not
let me guess
What star sign are you? No, let me guess.

you can probably guess, you have probably guessed
You can probably guess how she reacted!

you'll never guess where, who, how, etc.
You'll never guess who I saw yesterday!

Guess is used with these nouns as the object:
answer, identity, password, reason, size, truth