An Etymological Dictionary of Astronomy and Astrophysics

An adverb meaning without others or anything further; alone; solely; exclusively. → if and only if.

Etymology (EN): M.E., from O.E. anlic, from ân, → one.

Etymology (PE): Ivâz, from Mid.Pers. êvâz/êvâc, from Proto-Iranian *aiua-ka-; cf. Pers. yek, → one.
Tanhâ “only,” from Mid.Pers. tanihâ “alone,” literally “by one person,” from tan “body, person;” Av. tanu- “body, person;” cf. Skt. tanu- “body, person;” perhaps related to Proto-Iranian *tan-, PIE root *ten- “to extend, stretch,” → tension.