Coherent means holding together — the parts fit, the argument follows, one sentence leads to the next. A coherent plan, a coherent explanation, a coherent piece of writing.
It is also used of people, and there it means able to speak clearly and make sense: he was barely coherent after the crash. Two words sit close and are not the same. Cohesive is about the physical or social sticking together of a group or a substance; coherent is about the logic. And consistent means not contradicting itself over time, which a thing can be while remaining incoherent. In physics, coherent light is light whose waves stay in step, which is exactly the same idea applied to something you can measure.
1adjectivecoherentLogically connected, with the parts fitting together.
“It is the first coherent explanation anyone has offered.”
synonyms: logical, consistent, lucid
2adjectiveableOf a person, able to speak clearly and be understood.
“He was not coherent enough to give a statement.”
3adjectivelightOf light or waves, staying in step.
“A laser produces coherent light.”
coherent is a quality of holding together.
Latin cohaerere is co-, together, plus haerere, to stick — the same verb behind adhere and hesitate, which is a mind sticking. A coherent argument is one whose parts stick to each other, and an incoherent one has come apart.
Latin
cohaerēns
Middle French
coherent
English, today
coherent
From Middle French coherent, from Latin cohaerēns. From Middle French coherent, from Latin cohaērēns, from co- + haereō. by surface analysis, cohere + -ent.
Etymology from Wiktionary, CC BY-SA