Ef

As defined by A Concise Dictionary of Old Icelandic (Geir Zoëga):

ef Old Icelandic word can mean:

ef

I)

ef

(older form if), conj.

ef

1) if, in case (aldri hefðir þú í borgina komit, ef ek hefða vitat); in poetry generally with subj.; vega þú gakk, ef vreiðr séir (sér), if thou be wroth;

ef

2) = hvárt, if, whether (Egill spurði, ef hann vildi upp ór gröfinni);

ef

3) as a relat. part., sá ef = sá er (rare).

ef

II)

ef

n. doubt; ef er á e-u, it is doubtful; ekki er til efs, at, it cannot be doubted that; útan ef, without doubt.

Possible runic inscription in Younger Futhark:ᛁᚠ