Other forms: customs
A custom is a way of doing things that is usual in a community. Nobody wrote it down, and everybody knows it.
It sits between a habit, which belongs to one person, and a law, which is enforced. Local custom, an old custom, the custom of the country. The plural has a separate life at borders, since customs is the office that inspects what you bring in. As an adjective it means made to order, so a custom kitchen is built for one house, and customise means to alter something to suit you.
1nouncustomA traditional and widely accepted way of behaving in a society.
“It is the custom here to bring a small gift.”
2adjectivespeciallyMade specially for one customer.
“He ordered a custom frame for the picture.”
Too few real examples of this word to estimate which sense is commonest.
A custom is what you have grown used to. Latin cōnsuēscō is con, with, plus suēscō, to become accustomed, so the word names the habit rather than the rule.
Proto-Indo-European
*dʰeh₁-
Latin
consuetudo
Anglo-Norman
coustume
Middle English
custume
English, today
custom
Built from
From Middle English custume, borrowed from Anglo-Norman coustume, inherited from Latin consuetudo, a noun derived from cōnsuēscō, from con- (“with”) + suēscō (“become used or accustomed to”). Displaced native Old English ġewuna and sidu. a doublet of costume and consuetude and kastom. The adjectival form first appears c. 1830.
Etymology from Wiktionary, CC BY-SA