Ambiguous is applied only to spoken or written statements; equivocal has other applications. Equivocal is sometimes, tho more rarely, used in this sense.

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

Example sentences

vague I deal in facts and figures, not vague impressions.
ambiguous The main feature of this scheme is still ambiguous.
evasive Yanni didn't maintain eye contact and was evasive.
indeterminate The results of the study are indeterminate.
uncertain Tom told me that he's uncertain what he should do.
doubtful It's doubtful whether Tom will be able to do that.

Popularity over time

Word	1850 → 2019	Trend
equivocal		steady
vague		steady
ambiguous		rising
evasive		steady
indeterminate		steady
uncertain		steady

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

By length

4 letters: hazy²
5 letters: mixed¹, vague¹, shady², fuzzy², fishy², murky²
6 letters: double², unsure², turbid²
7 letters: unclear², obscure², dubious³, evasive³
8 letters: doubtful²
9 letters: uncertain³, ambiguous⁴, undecided⁴, enigmatic⁴
10 letters: suspicious³, indefinite⁴, precarious⁴, indistinct³, perplexing³
11 letters: incongruous⁴, enigmatical
12 letters: questionable⁴
13 letters: unpredictable⁵, indeterminate⁵

The small number after each word is its number of syllables (hazy² = 2 syllables).

In other languages

Français: équivoque
Italiano: equivoco
Español: equívoco