(idiomatic) An issue or topic which is not of direct significance to a primary concern.

(chemistry) Any of a number of compounds that exhibit structural isomerism

(chemistry) Either of a pair of geometric isomers, one having the cis- and one having the trans- configuration.

(chemistry, dated, deprecated by IUPAC) either the cis- or trans- isomer of a compound that exhibits geometric isomerism

(chemistry) Any one of a number of compounds that exhibit optical isomerism.

(organic chemistry) An unsaturated hydrocarbon, C₅H₈, that is readily polymerized; natural rubber (caoutchouc) is cis-1,4-polyisoprene, and trans-1,4-polyisoprene is present in gutta-percha and balata; it is the structural basis for the terpenes.

That is the way things happen / Certain things cannot be changed, helped or improved; struggle and objection are pointless.

(chemistry) any isomer that differs from another isomer only in the position of a substituent, or of a double or triple bond

An archipelago and overseas territory of the United Kingdom in the southern Pacific Ocean.

It is allowable to retaliate against an enemy's dirty tricks by using the same ones against them. / Taking turns is morally right.