What connects the words nexus, annex(e) and connection?

A nexus [ˈnɛksəs] is form or state of connection; a connected group, network or web; or a centre or focus of something. It comes from Latin nexus (bound, tied, fastened, connected, interwoven), from nectō (to connect, interweave, attach, bind, tie, oblige), possibly from nōdus (knot, bond, obligation) and/or nassa (a narrow-necked basket for catching fish) [source].

Apparently in Ancient Rome, a nexus was a person who had contracted a nexum or obligation of such a kind that, if they failed to pay, their creditor could compel them to work as a servant until the debt was paid. This practice was abolished in 326 BC [source].

If there is more than one nexus, there are several nexuses, nexusses or nexi. The plural in Latin is nexūs or nexûs, not nexi, by the way. Do you have a preferred plural for this word?

Related words include nexo (nexus, connection, sense, coherence) in Portuguese, nexo (link, connection, nexus) in Spanish and nexe (nexus, connection, link) in Catalan [source].

The word annex(e) (an addition, extension, appendix) also comes from the same roots, via French annexe (annex(e), appendix), from Latin annexus (tied, fastened, bound, related by blood), from annectō / adnectō (to bind, tie to, connect, annex), from ad- (to) and nectō (to connect, etc) [source].

Related words include anejo (accompaniment, affix) and anexar (to annex, attach) in Spanish, and annettere (to attach, add, annex, consolidate) in Italian [source].

Another connected word is the word connection, which comes from Middle English connexioun (connection), from Latin connexionem, from cōnexiō (junction, meeting, connection), from cōnectō (to connect, link, fasten together) from con- (with) and nectō (to connect, etc) [source].

Related words include connexe (closely related, connected) in French, connesso (connected, associated, linked, related) in Italian and conex (connected) in Romanian [source].