The word(s) "conjecture" appears 8 time(s) in 7 verse(s) in Quran in Abdullah Yusuf Ali translation.

(1) And there are among them illiterates, who know not the Book, but (see therein their own) desires, and they do nothing but conjecture.

(2) That they said (in boast), "We killed Christ Jesus the son of Mary, the Messenger of Allah";- but they killed him not, nor crucified him, but so it was made to appear to them, and those who differ therein are full of doubts, with no (certain) knowledge, but only conjecture to follow, for of a surety they killed him not:-

(3) Wert thou to follow the common run of those on earth, they will lead thee away from the way of Allah. They follow nothing but conjecture: they do nothing but lie.

(4) Those who give partners (to Allah) will say: "If Allah had wished, we should not have given partners to Him nor would our fathers; nor should we have had any taboos." So did their ancestors argue falsely, until they tasted of Our wrath. Say: "Have ye any (certain) knowledge? If so, produce it before us. Ye follow nothing but conjecture: ye do nothing but lie."

(5) And they say: "What is there but our life in this world? We shall die and we live, and nothing but time can destroy us." But of that they have no knowledge: they merely conjecture:

(6) These are nothing but names which ye have devised,- ye and your fathers,- for which Allah has sent down no authority (whatever). They follow nothing but conjecture and what their own souls desire!- Even though there has already come to them Guidance from their Lord!

(7) But they have no knowledge therein. They follow nothing but conjecture; and conjecture avails nothing against Truth.