side chain

1(organic chemistry) That part of a molecule attached to some core structure; a radical.
2(biochemistry) Any of the variable parts of amino acids that extend from the peptide backbone in proteins; they are referred to as R-groups, which branch off the backbone at the alpha carbon (Cα).
3audioAuxiliary audio input fed to a synthesizer etc. and used to selectively trigger an effect.
4(cryptocurrencies) A separate blockchain attached to a parent blockchain (mainchain) to extend its functionalities.
5(rail transport) On some railways, a chain fitted on both sides of a centre coupler or buffer at each end of a rail vehicle, which has a hook for connection to a corresponding chain on the next vehicle in a train.