leyǵ-
“to bind, to league”bind, tie, league
Root for binding/tying, yielding Latin ligare (to bind), English league, ligament, religion.
Discussion
The PIE root *leyǵ- (to bind, to tie, to fasten with a ligature) produced the Latin vocabulary of binding obligations and the English vocabulary of alliances — the concept that to be bound together is to be allied.
Latin ligāre (to bind, to tie) continues the root directly and gave English: ligament (a binding tissue), ligature (a binding thread — in surgery and typography), league (a binding agreement between parties — both political and sporting), liable (bound by obligation), rely (re-ligāre, to bind back to — to be bound to someone by trust), oblige (ob-ligāre, to bind toward — to constrain by duty), and ally (ad-ligāre, to bind to).
The word religion may derive from this root through Latin religiō, if interpreted as re-ligāre ("to bind back" — to reconnect with the divine). This etymology, favoured by Lactantius and later Christian writers, competes with Cicero's derivation from relegere ("to re-read, to go over carefully" — see *leǵ- for the reading/gathering root). The debate is ancient and unresolved, but the ligāre etymology has dominated popular understanding: religion as a binding-back to God.
Gothic ga-ligan (to lie together) and Old English licgan (to lie) may connect through a related root, though the exact relationship is debated.
The root's institutional legacy is profound: a league, an alliance, an obligation, and (possibly) a religion are all bindings — social structures conceived as ropes or ties that hold groups together. Compare *bʰendʰ- (to bind, to tie — the related root that gave English bind/bond) for the parallel Germanic vocabulary of binding.
Notes
Pokorny 668. English league, ligature, oblige, religion, rely.