v. 1
To reach a partly (or totally) unconfirmed conclusion; to engage in conjecture; to speculate.
We can only guess at what was going through her mind.
v. 2
To solve by a correct conjecture; to conjecture rightly.
You guessed the right answer!
v. 3
To suppose, to imagine (introducing a proposition of uncertain plausibility).
That album is quite hard to find, but I guess you could try ordering it online.
n. 1
A prediction about the outcome of something, typically made without factual evidence or support.
If you don't know the answer, take a guess.

Related words

Word family: guesstimate guessable
Phrases: wild guess educated guess anyone's guess anybody's guess guess what intelligent guess uneducated guess stab a guess

Forms

Plural: guesses → suppositions, hypotheses, speculations, presumptions…
Past participle: guessed
e.g. guessed → supposed, reckon'd, surmised, imagined…

Choose the right word

Guess or Hypothesis?

A hypothesis may be termed a comprehensive guess. A guess is a swift conclusion from data directly at hand, and held as probable or tentative, while one confessedly lacks material for absolute certainty.

J. C. Fernald, English Synonyms and Antonyms (1914)

Example sentences

imagine We are never as happy or as unhappy as we imagine.
suppose I suppose we're a little too indulgent to the dog.
reckon What do you reckon the voter turnout will be today?
surmise "What do you think of my theory?" "It is all surmise."

Popularity over time

Word	1850 → 2019	Trend
guess		rising
imagine		rising
suppose		rising
reckon		rising
surmise		steady

Use in printed books, per decade from 1850 to 2019.

By length

4 letters: shot¹
5 letters: judge¹, solve¹, fancy², opine²
6 letters: assume², divine², hazard², reckon², fathom²
7 letters: believe², imagine³, suppose², suspect², pretend², venture², presume², surmise²
8 letters: estimate³, surmisal
9 letters: suspicion³, speculate³
10 letters: prediction³, hypothesis⁴, conjecture³
11 letters: speculation⁴, calculation⁴, approximate⁴, presumption³, supposition⁴, hypothesize⁴, hypothesise, hypothetise

The small number after each word is its number of syllables (fancy² = 2 syllables).

In other languages

Français: deviner
Español: adivinar
Deutsch: enträtseln
Català: endevinar