An Etymological Dictionary of Astronomy and Astrophysics

To stretch out; draw out to the full length; to enlarge the scope of; to increase the length or duration of.

Etymology (EN): From O.Fr. estendre, from L. extendere “stretch out,” from → ex- “out” + tendere “to stretch,” see below.

Etymology (PE): Ostanidan, from os-, → ex- + tanidan as in Av. ustāna- “stretched out” (ustāna-zasta- “with outstretched hands”), cf. Skt. uttāná- “stretched out, spread out.” Mod.Pers. tanidan “to spin, twist, weave;” Mid.Pers. tanitan, from
Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend," tanoti “stretches,” tantram “loom;” Gk. teinein “to stretch, pull tight;” L. tendere “to stretch;”
PIE base *ten- “to stretch.”